Merge pull request #376 from reaperhulk/more-engine-methods

Add the rest of the engine methods
add urandom engine and set it as default RAND method.

This is a proposed solution to the OpenSSL fork problem.
allow the backend to register/unregister the engine via methods
add urandom engine register/unregister tests

also rename some variables in the urandom engine for easier comparison
fix fd int check, remove stray comedy printf()
remove unneeded INT_MAX check
additional check to verify the ENGINE_new doesn't return null