message catalogs: fix comment lines, also remove linux hack in merge.c

According to the spec, blank lines in message catalogs or lines
beginning with '$ ' are valid comments.

However, there were many cases where lines in the message catalogs
contained just a single '$', without the required space after it.

Under linux, this caused 126766 error lines (in my builds) of the
form:

... unknown directive `': line ignored

This also causes gencat to exit with a non-0 exit code.  Even though
gencat says it ignores the line, it really doesn't.

An early porting change to programs/localized/util/merge.c was made to
ignore this return value on linux.  This hack has now been removed.

Build logs are a lot smaller and cleaner now.

cde/programs/localized/C/app-defaults/Dtterm.tmsg

@@ -30,7 +30,7 @@ $ Message 1 can be translated.  This message lists the 7 interface fonts
 $ offered to the user via the style manager (dtstyle).  They are the
 $ seven interface fonts that are defined for this locale and should
 $ be specified as XmFontLists containing XFontSets.
-$
+$ 
 1 -dt-interface user-medium-r-normal-xxs*-*-*-*-*-m-*:\\n\\\n\
 -dt-interface user-medium-r-normal-xs*-*-*-*-*-m-*:\\n\\\n\
 -dt-interface user-medium-r-normal-s*-*-*-*-*-m-*:\\n\\\n\