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/es_ES.ISO8859-1/app-defaults/Dticon.tmsg

@@ -79,22 +79,22 @@ $
 
 10 "Alt<key>F4"
 
-$
+$ 
 $  Message 11, 12. Menu label is "New".
 11 "Ctrl+N"
 12 "Ctrl<Key>N"
 
-$
+$ 
 $  Message 13, 14. Menu label is "Open".
 13 "Ctrl+O"
 14 "Ctrl<Key>O"
 
-$
+$ 
 $  Message 15, 16. Menu label is "Save".
 15 "Ctrl+S"
 16 "Ctrl<Key>S"
 
-$
+$ 
 $  Message 17, 18. Menu label is "Save As".
 17 "Ctrl+A"
 18 "Ctrl<Key>A"