Erlang: correctly handle additional LibDirs

The compile function expects a list of paths in the LibDirs parameter,
however when calling erlang_check_file.erl with an additional path (for
example when using the "g:syntastic_erlc_include_path" option), a
string would be passed instead. Because strings in Erlang are lists,
each character of the string would have been interpreted as a lib path.
Merge pull request #1182 from russss/master

Erlang: correctly handle additional LibDirs