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/it_IT.ISO8859-1/msg/dthello.msg

@@ -58,7 +58,7 @@ $    DO NOT TRANSLATE THESE MESSAGES
 
 $ Messages 4 and 5 are both used when there is a syntax error on
 $ the command line invoking dthello
-$
+$ 
 4 Sintassi: %s [-display <schermo>] [-fg <colore>] [-bg <colore>]\\\n
 5 [-font <font>] [-string <messaggio>] [-file <nome>] [-timeout <secondi>]\n