Merge pull request #369 from daimrod/fix-compilation-find-file

* projectile.el (projectile-mode): Fix f71b5f7
[Fix #370] A temp workaround

advice-add and advice-remove are only available in Emacs 24.4.
Enable defining compilation/test commands in file-/dir-local vars.

They should be safe as long as they're strings.
Add Cargo.toml as a project root file
Merge pull request #373 from tomjakubowski/patch-1

Add Cargo.toml as a project root file
Add helm to allowable completion systems
Merge pull request #371 from immerrr/mark-cmds-safe-if-strings

Enable defining compilation/test commands in dir-local vars
Check whether helm completion function is defined
Merge pull request #378 from alanpearce/helm

Add helm to allowable completion systems
Update projectile.el
Merge pull request #380 from peterhoeg/patch-1

Update projectile.el
Make less calls to file-truename.

Makes things very slow when using tramp otherwise, this is a partial
fix. It might be a good idea to not call file-truename here at all on
remote file systems or implement a file-truename cache.
Merge pull request #383 from thomasf/master

Make less calls to file-truename.
Demote errors to messages when trying to load a TAGS file.
Merge pull request #381 from jasonm23/ignore-ctags-load-error

Ignore errors when loading a tags file.
Call error if the tags command failed.

Fixes https://github.com/bbatsov/projectile/issues/377
Merge pull request #379 from Wilfred/master

Call user-error if the tags command failed.
Use `defadvice' rather than the new `nadvice` interface which is only
available in trunk. This fixes f71b5f7.

* projectile.el (projectile-compilation-find-file): Convert to `defavice'.
                (projectile-mode): Use ad-(de)activate.