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/zh_CN.dt-eucCN/msg/libDtMail.msg

@@ -230,7 +230,7 @@ $ // DTME_CannotRenameNewMailboxFileOverOld
 $ // DTME_InternalAssertionFailure
 71 "An internal error has occurred within this application.\nThere is no way to recover and continue from this error.\nError condition: %s\n"
  
-$
+$ 
 $ Strings from libDtMail/Common/DtMailValuesBuiltin.C
 
 $set 2