Insure parse_version does not return tuple (resolves #476)

* Insure min_version does not return tuple (resolves #476)

* Mention minimal setup tools version in error message

* Improve version checking error message

setup.py

@@ -21,8 +21,12 @@
 from version import version
 from pkg_resources import parse_version, require, DistributionNotFound
 
+
 def check_provided(distribution, min_version, max_version=None, optional=False):
     min_version = parse_version(min_version)
+    if isinstance(min_version, tuple):
+        raise RuntimeError("Setuptools version 8.0 or newer required. Update by running "
+                           "'pip install --upgrade setuptools'")
     if max_version is not None:
         max_version = parse_version(max_version)