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/dtpdm/dtpdm.msg

@@ -41,7 +41,7 @@ $
 $ 	Message numbers 1-4 appear in the page orientation option menu
 $ 	and indicate how the resulting printed page should be
 $ 	oriented.
-$
+$ 
 $     */
 1 Portrait
 2 Landscape
@@ -61,7 +61,7 @@ $		    English book) or right to left.
 $	Tumble  ->  print both sides such that the resulting output is
 $		    intended for the reader to turn pages in a
 $		    vertical direction; top to bottom or bottom to top
-$
+$ 
 $     */
 5 Simplex
 6 Duplex