CLIENT CONFIGURATION.

At startup, MySQL server/client programs do not read
configuration file pointed by MYSQL_HOME environment
variable.

This happened as, this environment variable was
handled by a different variable (DEFAULT_HOME_ENV)
in the code, which was ne'er initialized.

Fixed by changing it to MYSQL_HOME.


mysys/default.c:
  BUG 11766219 : 59280: $MYSQL_HOME IS NOT USED FOR THE
                 CLIENT CONFIGURATION.
  
  In the current build environment, the variable
  DEFAULT_HOME_ENV is no more found being initialized
  to MYSQL_HOME (as was the case earlier). Changed the
  variable name to MYSQL_HOME.