Add possibility to specify a rebar file as parameter in erlang_check_file.erl

I want to use lib_dirs and sub_dirs from rebar file and run compile with
this paths. So I search for the next rebar.config file and pass this in
g:syntastic_erlc_include_path.

see: https://github.com/scrooloose/syntastic/issues/685
Merge pull request #757 from nougad/erlang_rebar

Add possibility to specify a rebar file as parameter in erlang_check_file.erl