Make the validate-extensions.py hook script case insensitive.
Make the validate-extensions.py hook script case insensitive.

* tools/hook-scripts/validate-extensions.py
  (validate_added_extensions): Normalize file extention to lower case
    for comparison against...
  (main): ...user-provided extension which are now also normalized to
    lower case.

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion