TBD: Refactor syntastic deactivation / fix for EclimFileTypeValidate=0

Add eclim#lang#isFiletypeValidationEnabled and
eclim#lang#disableSyntasticIfValidationIsEnabled and call the latter
from filetype files.

TODO: this commit contains the change for php.vim only, but should get
used for the other filetypes, when accepted.

This pull request is meant for discussion - feel free to adopt it as you see it fits, or tell me how to change it.

The issue I had was that I ended up debugging Syntastic, trying to find out why the list of checkers ended up empty. It turned out that eclim forcefully set it, although I am using `g:EclimFileTypeValidate=0`.