Improvements to rtp management and start up.
Several changes:
 * For both Bundle and Plugin fixes the rtp ordering issues, ~/.vim should be first.
 * For Plugin, during vundle#begin/end block use delayed initialization to speed up.
 * After end() works, all plugins should be available.
 * Simply replacing documentation of vundle#rc with begin/end.
Merge branch 'rtp_changes' into next