Add syntax files from upstream vim repository

ftplugin/hgcommit.vim

@@ -0,0 +1,20 @@
+if !exists('g:polyglot_disabled') || index(g:polyglot_disabled, 'vim') == -1
+  
+" Vim filetype plugin file
+" Language:	hg (Mercurial) commit file
+" Maintainer:	Ken Takata <kentkt at csc dot jp>
+" Last Change:	2016 Jan 6
+" Filenames:	hg-editor-*.txt
+" License:	VIM License
+" URL:		https://github.com/k-takata/hg-vim
+
+if exists("b:did_ftplugin")
+  finish
+endif
+let b:did_ftplugin = 1
+
+setlocal nomodeline
+
+let b:undo_ftplugin = 'setl modeline<'
+
+endif