win: fixes for using vs 2013 toolchain

pylib/gyp/MSVSVersion.py

Index: pylib/gyp/MSVSVersion.py
diff --git a/pylib/gyp/MSVSVersion.py b/pylib/gyp/MSVSVersion.py
index 0ef427efab89838d753a768c62b078a487034172..956fa011610966e3fbe471c2dcf821e6e4fd8c80 100644
--- a/pylib/gyp/MSVSVersion.py
+++ b/pylib/gyp/MSVSVersion.py
@@ -391,9 +391,9 @@ def SelectVisualStudioVersion(version='auto'):
   override_path = os.environ.get('GYP_MSVS_OVERRIDE_PATH')
   if override_path:
     msvs_version = os.environ.get('GYP_MSVS_VERSION')
-    if not msvs_version or 'e' not in msvs_version:
+    if not msvs_version:
       raise ValueError('GYP_MSVS_OVERRIDE_PATH requires GYP_MSVS_VERSION to be '
-                       'set to an "e" version (e.g. 2010e)')
+                       'set to a particular version (e.g. 2010e).')
     return _CreateVersion(msvs_version, override_path, sdk_based=True)
   version = str(version)
   versions = _DetectVisualStudioVersions(version_map[version], 'e' in version)