Add a check for the error messages variable so that users can specify their own error format.
Checkers cleanup.

Elliminates duplicate code.
Brings gcc cpp, objc, and ada checkers in synch with c.
Minor bug fixes.
Bug fix.
Another bug fix.
Merge pull request #536 from trprice/master

Make.vim - Check g:syntastic_c_errorformat so that users can provide their own error format
Merge pull request #571 from lcd047/cleanup_dupes

Checkers cleanup