Add new clang-tidy and clang-check checkers

These checkers use an existing compilation database so that the actual
flags used in the compile are used in the check.
Merge remote-tracking branch 'bbanier/t/clang_tools' into clang_tools
Clang tools: work without a compilation database.  Cleanup.
Clang tools: missing space.
Clang tools: check exit codes.
A cleaner way to kill default variables.
README: add a note about Python 3.
README: typo.
Don't assume loclists have vcol fields.
SCSS-Lint: new error codes.
Do not `expand()` shell vars

This is especially important when testing/using variables that do not
exist, because then a new shell is spawned by Vim.
But since they should be available already in Vim from the (shell) env
there is no point in doing so.

See also: http://www.reddit.com/r/vim/comments/2el2zo
Merge pull request #1170 from blueyed/dont-call-expand-on-shellvar

Do not `expand()` shell vars
Cursor columns: fix redraw.
New checker for PHP: PHPLint.
PHPLint: fix syntax highlighting.
Bump version number.
Add support for maven customizations