configure.in:

  AC_ARG_WITH inside "if" sometimes gives unexpected result,
  --with-fast-mutexes was not ignored when --with-debug given

configure.in

@@ -1608,18 +1608,20 @@ else
   CXXFLAGS="$OPTIMIZE_CXXFLAGS -DDBUG_OFF $CXXFLAGS"
 fi
 
-if test "$with_debug" = "no"
-then
-  AC_ARG_WITH([fast-mutexes],
+AC_ARG_WITH([fast-mutexes],
 	    AC_HELP_STRING([--with-fast-mutexes], 
 	    [Compile with fast mutexes (default is disabled)]),
 	    [with_fast_mutexes=$withval], [with_fast_mutexes=no])
-fi
 
-if test "$with_fast_mutexes" = "yes"
+if test "$with_fast_mutexes" != "no"
 then
+  if test "$with_debug" != "no"
+  then
+    AC_MSG_WARN(['--with-fast-mutexes' ignored when '--with-debug' is given])
+  else
     AC_DEFINE([MY_PTHREAD_FASTMUTEX], [1], 
 	      [Define to 1 if you want to use fast mutexes])
+  fi
 fi
 
 # Force static compilation to avoid linking problems/get more speed