Bug #30759  	mysql_install_db fails to set $extra_bindir properly in all cases.


scripts/mysql_install_db.sh:
  Preliminary fix for
     Bug #30759  	mysql_install_db fails to set $extra_bindir properly in all cases.
  
  Provided by Daniel for the 5.1.22-rc build, to be superseded by a better patch when that is available.