patch 8.1.0111: .po files do not use recommended names

Problem:    .po files do not use recommended names.
Solution:   Give a warning if the recommended name is not used.  Accept the
            recommended name for conversion. (Christian Brabandt, Ken Takata)
diff --git a/src/po/check.vim b/src/po/check.vim
index 24c4d79..672b4f3 100644
--- a/src/po/check.vim
+++ b/src/po/check.vim
@@ -173,12 +173,37 @@
   " We allow for a stray plural header, msginit adds one.
 endif
 
+" Check that 8bit encoding is used instead of 8-bit
+let cte = search('^"Content-Transfer-Encoding:\s\+8-bit', 'n')
+let ctc = search('^"Content-Type:.*;\s\+\<charset=[iI][sS][oO]_', 'n')
+let ctu = search('^"Content-Type:.*;\s\+\<charset=utf-8', 'n')
+if cte
+  echomsg "Content-Transfer-Encoding should be 8bit instead of 8-bit"
+  " TODO: make this an error
+  " if error == 0
+  "   let error = cte
+  " endif
+elseif ctc
+  echomsg "Content-Type charset should be 'ISO-...' instead of 'ISO_...'"
+  " TODO: make this an error
+  " if error == 0
+  "   let error = ct
+  " endif
+elseif ctu
+  echomsg "Content-Type charset should be 'UTF-8' instead of 'utf-8'"
+  " TODO: make this an error
+  " if error == 0
+  "   let error = ct
+  " endif
+endif
+
 
 if error == 0
   " If all was OK restore the view.
   call winrestview(wsv)
   echomsg "OK"
 else
+  " Put the cursor on the line with the error.
   exe error
 endif