Add a missing statement, add licensing info and correct coding style

mysys/default_modify.c:
  Add forgotten opt_applied= 1 statement. Because of this adding new options to sections didn't work.
  Extended function comment, addded licencing info and fixed coding style. With current patch only
  the first occurence of the option in a section is changed. According to monty, all options should be changed
  instead. This change is to appear in the next patch.

mysys/default_modify.c

+/* Copyright (C) 2005 MySQL AB
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 2 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */
+
+#include "my_global.h"
+#include "mysys_priv.h"
+#include "m_string.h"
+#include <my_dir.h>
+
+#define BUFF_SIZE 1024
+
+#ifdef __WIN__
+#define NEWLINE "\r\n"
+#define NEWLINE_LEN 2
+#else
+#define NEWLINE "\n"
+#define NEWLINE_LEN 1
+#endif
+
+static char *add_option(char *dst, const char *option_value,
+			const char *option, int remove_option);
+
+
 /*
   Add/remove option to the option file section.
 
@@ -15,6 +50,8 @@
     into a buffer. Then we look for the option within this section and
     change/remove it. In the end we get a buffer with modified version of the
     file. Then we write it to the file, truncate it if needed and close it.
+    Note that there is a small time gap, when the file is incomplete,
+    and this theoretically might introduce a problem.
 
   RETURN
     0 - ok
@@ -22,24 +59,6 @@
     2 - cannot open the file
 */
 
-#include "my_global.h"
-#include "mysys_priv.h"
-#include "m_string.h"
-#include <my_dir.h>
-
-#define BUFF_SIZE 1024
-
-#ifdef __WIN__
-#define NEWLINE "\r\n"
-#define NEWLINE_LEN 2
-#else
-#define NEWLINE "\n"
-#define NEWLINE_LEN 1
-#endif
-
-static char *add_option(char *dst, const char *option_value,
-			const char *option, int remove_option);
-
 int modify_defaults_file(const char *file_location, const char *option,
                          const char *option_value,
                          const char *section_name, int remove_option)
@@ -47,7 +66,7 @@ int modify_defaults_file(const char *file_location, const char *option,
   FILE *cnf_file;
   MY_STAT file_stat;
   char linebuff[BUFF_SIZE], *src_ptr, *dst_ptr, *file_buffer;
-  uint optlen, optval_len, sect_len, nr_newlines= 0;
+  uint opt_len, optval_len, sect_len, nr_newlines= 0;
   my_bool in_section= FALSE, opt_applied= 0;
   DBUG_ENTER("modify_defaults_file");
 
@@ -58,7 +77,7 @@ int modify_defaults_file(const char *file_location, const char *option,
   if (my_fstat(fileno(cnf_file), &file_stat, MYF(0)))
     goto err;
 
-  optlen= (uint) strlen(option);
+  opt_len= (uint) strlen(option);
   optval_len= (uint) strlen(option_value);
 
   /*
@@ -68,15 +87,16 @@ int modify_defaults_file(const char *file_location, const char *option,
   if (!(file_buffer= (char*) my_malloc(sizeof(char) *
                                        (file_stat.st_size +
                                         /* option name len */
-					optlen +
+                                        opt_len +
                                         /* reserve space for newline */
                                         NEWLINE_LEN +
                                         /* reserve for '=' char */
                                         1 +
                                         /* option value len */
                                         optval_len +
-					/* The ending zero plus some safety */
-					FN_REFLEN), MYF(MY_WME))))
+                                        /* The ending zero */
+                                        1), MYF(MY_WME))))
+
     goto malloc_err;
 
   sect_len= (uint) strlen(section_name);
@@ -94,10 +114,11 @@ int modify_defaults_file(const char *file_location, const char *option,
       continue;
     }
 
-    if (!opt_applied && in_section && !strncmp(src_ptr, option, optlen) &&
-	(*(src_ptr + optlen) == '=' ||
-	 my_isspace(&my_charset_latin1, *(src_ptr + optlen)) ||
-	 *(src_ptr + optlen) == '\0'))
+    /* correct the option */
+    if (!opt_applied && in_section && !strncmp(src_ptr, option, opt_len) &&
+        (*(src_ptr + opt_len) == '=' ||
+         my_isspace(&my_charset_latin1, *(src_ptr + opt_len)) ||
+         *(src_ptr + opt_len) == '\0'))
     {
       dst_ptr= add_option(dst_ptr, option_value, option, remove_option);
       opt_applied= 1;
@@ -108,8 +129,9 @@ int modify_defaults_file(const char *file_location, const char *option,
       if (in_section && !opt_applied && *src_ptr == '[')
       {
         dst_ptr= add_option(dst_ptr, option_value, option, remove_option);
-
+        opt_applied= 1;           /* set the flag to do write() later */
       }
+
       for (; nr_newlines; nr_newlines--)
         dst_ptr= strmov(dst_ptr, NEWLINE);
       dst_ptr= strmov(dst_ptr, linebuff);