Allowing for custom lib and conf file placement

Hi there,

I have created a pull request that allows for custom config overrides and jar placement in the lib dirs. The existing custom overlay feature is quite powerful and I wanted to re-use the ant build system instead of relying on maven. This change allows for complete isolation of "custom" code from the openfire source tree and improves maintainability.

You can find the pull request for the build.xml and documentation changes at https://github.com/igniterealtime/Openfire/pull/64.

Looking forward for feedback and suggestions.

Thanks,

Shawn