There are two main idea of this fix:
  - introduce a common function for server and client to split user value
    (<user name>@<host name>) into user name and host name parts;
  - dump DEFINER clause in correct format in mysqldump.


BitKeeper/etc/ignore:
  added client/my_user.c libmysqld/my_user.c sql/my_user.c
client/Makefile.am:
  Use my_user.c in linking of mysqldump executable.
client/mysqldump.c:
  Fix for BUG#15110(mysqldump --triggers: does not include DEFINER clause)
include/Makefile.am:
  Add my_user.c
include/mysql_com.h:
  Introduce a constant for max user length.
libmysqld/Makefile.am:
  Add my_user.c
mysql-test/r/mysqldump.result:
  Update result file.
sql-common/Makefile.am:
  Add my_user.c
sql/Makefile.am:
  Add my_user.c
sql/sp.cc:
  Use constant for max user length.
sql/sp_head.cc:
  Use common function to parse user value.
sql/sql_acl.cc:
  Use constant for max user length.
sql/sql_parse.cc:
  Use constant for max user length.
sql/sql_show.cc:
  Use constant for max user length.
sql/sql_trigger.cc:
  Use constant for max user length.
include/my_user.h:
  A header file for parse_user().
sql-common/my_user.c:
  A new file for parse_user() implementation.