Ensure we call tag_to_version

Closes #61

Author: brianmay

setuptools_scm/version.py

@@ -78,7 +78,7 @@ def format_choice(self, clean_format, dirty_format):
 
 
 def meta(tag, distance=None, dirty=False, node=None, **kw):
-    if parse_version is not None and not isinstance(tag, SetuptoolsVersion):
+    if SetuptoolsVersion is None or not isinstance(tag, SetuptoolsVersion):
         tag = tag_to_version(tag)
     trace('version', tag)