ext: Disable extension if a dependency isn't of the correct version

Fixes #657

docs/changelog.rst

@@ -4,6 +4,14 @@ Changelog
 
 This changelog is used to track all major changes to Mopidy.
 
+
+v0.18.1 (UNRELEASED)
+====================
+
+- Disable extension instead of crashing if a dependency has the wrong
+  version. (Fixes: :issue:`657`)
+
+
 v0.18.0 (2014-01-19)
 ====================
 

mopidy/ext.py

@@ -222,6 +222,12 @@ def validate_extension(extension):
             'Disabled extension %s: Dependency %s not found',
             extension.ext_name, ex)
         return False
+    except pkg_resources.VersionConflict as ex:
+        found, required = ex.args
+        logger.info(
+            'Disabled extension %s: %s required, but found %s at %s',
+            extension.ext_name, required, found, found.location)
+        return False
 
     try:
         extension.validate_environment()