vim-plugins: honor the plugin manager re filetype and syntax

Currently, all the filetype and syntax are enabled *after* all the plugins has
already been loaded. Whilst this is the case for Pathogen, it's not
recommended when using VAM.

This commit applies the recommendation for:
- VAM[0]: The filetype and syntax are enabled *before* the plugins are loaded.
- Pathogen[1]: The filetype and syntax are enabled *after* the plugins are loaded.
- Plug[2]: The filetype and syntax are automatically enabled.

[0]: d9e865f3c2 (recommended-setup)
[1]: a553410f1b/README.markdown (runtime-path-manipulation)
[2]: 2f5f74e5e6/README.md (usage)

pkgs/misc/vim-plugins/vim-utils.nix

@@ -208,6 +208,8 @@ let
       ''
         let &rtp.=(empty(&rtp)?"":',')."${vimPlugins.pathogen.rtp}"
         execute pathogen#infect('${pluginsEnv}/{}')
+
+        filetype indent plugin on | syn on
       '');
 
       /* vim-plug is an extremely popular vim plugin manager.
@@ -259,6 +261,8 @@ let
 
       in assert builtins.hasAttr "vim-addon-manager" knownPlugins;
       ''
+        filetype indent plugin on | syn on
+
         let g:nix_plugin_locations = {}
         ${lib.concatMapStrings (plugin: ''
           let g:nix_plugin_locations['${plugin.pname}'] = "${plugin.rtp}"
@@ -329,10 +333,12 @@ let
         set packpath-=~/.vim/after
         set packpath+=${packDir packages}
         set packpath+=~/.vim/after
+
+        filetype indent plugin on | syn on
       '');
 
   in writeText "vimrc" ''
-  " minimal setup, generated by NIX
+  " configuration generated by NIX
   set nocompatible
 
   ${vamImpl}
@@ -340,8 +346,6 @@ let
   ${plugImpl}
   ${nativeImpl}
 
-  filetype indent plugin on | syn on
-
   ${customRC}
   '';