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/dtmail/libDtMail/Common/libDtMail.msg

@@ -235,17 +235,17 @@ $ // DTME_InternalAssertionFailure
 
 $ "-NEW"
 $ // - DTME_ResourceParsingNoEndif
-$
+$ 
 72 "An error occurred while parsing the .mailrc resource file.\nThere is a conditional if statement that does not have a corresponding endif statement.\n"
   
 $ "-NEW"
 $ // - DTME_AlreadyOpened
-$
+$ 
 73 "This mail folder is already opened."
 
 $ "-NEW"
 $ // - DTME_OutOfSpace
-$
+$ 
 74 "No Space on Temporary Filesystem."
 
 $ "-NEW"
@@ -337,7 +337,7 @@ $ // - DTME_MailServerAccessInfo_MessageTooLarge
 96 "Skipping oversized message (%d bytes)."
   
 
-$
+$ 
 $ Strings from libDtMail/Common/DtMailValuesBuiltin.C
 
 $set 2
@@ -348,7 +348,7 @@ $  */
 1 "%C" 
   
 
-$
+$ 
 $ SockOpen error strings from libDtMail/Common/IO.C
 
 $ "-NEW"
@@ -361,7 +361,7 @@ $ "-NEW"
 4 "Error connecting to socket:  %s"
 
 
-$
+$ 
 $ FileShare error strings from libDtMail/Common/FileShare.C
 
 $ "-NEW"