The path hook used to load the module already in the `find_module` hook.
This caused different behaviour between Python 2.7 and 3.3, where the
former would call the `VimModuleLoader`, while Python 3.3 appears to
short-circuited this (because the module was loaded already).
This patch will now only find the module, but not load it in the
`find_module` hook.
Clipboard is implemented with platform-specific shell commands, and python is
implemented with the external plugin facility (rpc#* functions). The
script_host.py file(legacy python-vim emulation plugin) was moved/adapted from
the python client repository.
