Backport of the fix for BUG#40368 "mysqld_safe not honouring underscore same as dash on server options" from 6.0
(revision-id:guilhem@mysql.com-20090505113602-l12kxupeatve18dh).
Such bug led "mysqld_safe --core_file_size=#" to not work because mysqld_safe wouldn't recognize
that "ulimit -c" is needed; only --core-file-size=# worked. Same for --open_files_limit and other
options with _ where mysqld_safe needs to do something more than passing to mysqld.
Original fix by Erik Ljungstrom erik at ibiblio dot org ; slightly modified here.
Tested on all internally accessible Unix.