Allow additional filetypes to be registered to vimwiki files.

This options allow third party plugins to register and enable additonal
functionality by setting the filetype to vimwiki.other_ft.other_ft2 etc.
This option should be used with care since vimwiki functionality can be
overwritten by other plugins. See Issue #461 for an example use case.

autoload/vimwiki/u.vim

@@ -70,3 +70,28 @@ else
   endfunc
 endif
 
+
+" Sets the filetype to vimwiki
+" If g:vimwiki_filetypes variable is set
+" the filetype will be vimwiki.<ft1>.<ft2> etc.
+function! vimwiki#u#ft_set()
+  let ftypelist = vimwiki#vars#get_global('filetypes')
+  let ftype = 'vimwiki'
+  for ftypeadd in ftypelist
+    let ftype = ftype . '.' . ftypeadd
+  endfor
+  let &filetype = ftype
+endfunction
+
+
+" Returns: 1 if filetype is vimwiki, 0 else
+" If multiple fileytpes are in use 1 is returned only if the
+" first ft is vimwiki which should always be the case unless
+" the user manually changes it to something else
+function! vimwiki#u#ft_is_vw()
+  if split(&filetype, '\.')[0] ==? 'vimwiki'
+    return 1
+  else
+    return 0
+  endif
+endfunction