VCForPython27.msi安装后， 还显示error: Unable to find vcvarsall.bat

C:UserszpcAppDataLocalProgramsCommonMicrosoftVisual C++ for Python9.0VC

增加环境变量：

SET VCPYTHONPATH=C:UserszpcAppDataLocalProgramsCommonMicrosoftVisual C++ for Python9.0

254行增加以下内容：

if not productdir or not os.path.isdir(productdir):
        toolskey = "VCPYTHONPATH"
        toolsdir = os.environ.get(toolskey, None)

        if toolsdir and os.path.isdir(toolsdir):
            productdir = os.path.abspath(toolsdir)
            if not os.path.isdir(productdir):
                log.debug("%s is not a valid directory" % productdir)
                return None
        else:
            log.debug("Env var %s is not set or invalid" % toolskey)