BUG: Bug fix for Issue #5315

Added new logic to the fortran compiler version check to handle cases where
gcc is built with "--with-pkgversion=*some_string*, where *some_string*
contains numbers that might be incorrectly interpreted as a gcc version.

This includes some additional tests. All tests run successfully on Linux
Python version 2.7.8 and 3.4.2.
This isn't an accurate description of the function, it returns the string following the first nested parenthesis and takes as input a string following an opening parenthesis. Summary description should be one line, "private function" can be omitted since we know it is a function and the name begins with an underscore. I think would both clearer and simpler to have a function that took the full string and returned a string with nested content removed. Performance isn't an issue here.