Simplified module system

createModule got removed as it was unnecessary and caused issues by
doing its own cache checks independent of loadModule. Internal modules
are now the only globally cached modules, all other modules are only
cached by inheriting their parent modules cache.

Credits: Module specific cache and a few other diffs by Blaine Cook

http://github.com/blaine/node/commit/431662d25c0db3096deb5f679ca73b1dd6bb8ae5
http://romeda.org/blog/2010/01/hot-code-loading-in-nodejs.html
http://thread.gmane.org/gmane.comp.lang.javascript.nodejs/1994