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_TW.dt-eucTW/msg/libDtMail.msg

@@ -50,7 +50,7 @@ $set 1 libDtMail API set
 31 MD5 <20>杀卮胬曦毓丈涅诈拟肄苁·
 32 却真嘻仝如妃苴虽湘 "mail"
 
-$
+$ 
 $ Strings from libDtMail/Common/DtMailValuesBuiltin.C
 
 $set 2