Build PDF documentation.

def latex(self, force=False):
        """
        Build PDF documentation.
        """
        if sys.platform == 'win32':
            sys.stderr.write('latex build has not been tested on windows\n')
        else:
            ret_code = self._sphinx_build('latex')
            os.chdir(os.path.join(BUILD_PATH, 'latex'))
            if force:
                for i in range(3):
                    self._run_os('pdflatex',
                                 '-interaction=nonstopmode',
                                 'pandas.tex')
                raise SystemExit('You should check the file '
                                 '"build/latex/pandas.pdf" for problems.')
            else:
                self._run_os('make')
            return ret_code