Merge branch 'swekaj/fold-enhancements'
Folding: {Doc => Syn}Fold, after syntax/yacc.vim.

Avoid potential clash with user-defined commands. SynFold is specific to
the syntax.

Check if Vim has been compiled with 'folding' support as well.
Docker: Don't add the syntax file in the container.

Use host volumes to bind the plug-in directory as /var/php. This allows
us to change the syntax file without rebuilding the container.
PHP 5.6.0RC2
Fixed bug with highlighting things in closures.