Support for package namespaces
Replaced the (php).namespace feature with namespaces from the package.
In addition the (php).namespace feature didn't work as intended since
base classes was not properly referenced etc.
There are some major caveats
 - The compiler is not PSR-0 compliant
 - Nested types are still supported, but with underscores.
 - Currently no way to disable the feature
Re-worked namespaces, optional feature and fixes
Added optional feature to generate packaged based namespaces, defaults
to false to ensure compatibility.
Reverted multiple changes to apply more cleanly to master branch.
Fixed extensions
Merged upstream changes
Merge pull request #13 from onlinecity/master

protoc-gen-php: Support for package namespaces