instead of DATADIR.


include/config-win.h:
  Added checks for environment variable MYSQL_HOME
libmysql/Makefile.shared:
  Added checks for environment variable MYSQL_HOME
mysys/Makefile.am:
  Added checks for environment variable MYSQL_HOME
mysys/default.c:
  Removed checks for my.cnf file in datadir, instead added checking
  if my.cnf exists in environment variable MYSQL_HOME
scripts/mysqld_multi.sh:
  Added checks for my.cnf file in environment variable MYSQL_HOME,
  if exists.
scripts/mysqld_safe.sh:
  Added checks for my.cnf file in environment variable MYSQL_HOME,
  if exists.