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.

scripts/mysqld_safe.sh

@@ -160,7 +160,13 @@ parse_arguments() {
   fi
 
   for arg do
-    val=`echo "$arg" | sed -e "s;--[^=]*=;;"`
+    # the parameter after "=", or the whole $arg if no match
+    val=`echo "$arg" | sed -e 's;^--[^=]*=;;'`
+    # what's before "=", or the whole $arg if no match
+    optname=`echo "$arg" | sed -e 's/^\(--[^=]*\)=.*$/\1/'`
+    # replace "_" by "-" ; mysqld_safe must accept "_" like mysqld does.
+    optname_subst=`echo "$optname" | sed 's/_/-/g'`
+    arg=`echo $arg | sed "s/^$optname/$optname_subst/"`
     case "$arg" in
       # these get passed explicitly to mysqld
       --basedir=*) MY_BASEDIR_VERSION="$val" ;;