Modified string parentheses removal function.

The function _vstring_paren_strip was modified to incorporate some of the
changes suggested by @charris, such as improving the doc string and changing
some of the variable names.
Added extra gfortran check

If all of the string checks fail, an extra test was added thats runs gfortran with a
temp file and uses the output to generate the version. If this fails, then a
final generic error will get thrown.