Added `flymake-file-name-extension' and `flymake-file-sans-name-extension'.

This allows for more intelligent file name extension handling.

An example is [Drupal Coder Sniffer](https://drupal.org/project/coder) rules which enables special rules for ".tpl.php" files. For a file named "foo.tpl.php" flymake would created the temporary name "foo.tpl_flymake.php" and then the right rules would not apply.

The `flymake-file-name-extension' and `flymake-file-sans-name-extension' uses `flymake-allowed-file-name-masks` to identify which extension to consider.

This way I can add both ".tpl.php" and ".php" to `flymake-allowed-file-name-masks` and have [Drupal Coder Sniffer](https://drupal.org/project/coder) pickup the right rules.