Makefile generator: install loadable_modules like executables
Makefile generator: install loadable_modules like executables

This is necessary for the plugin tests.

Review URL: http://codereview.chromium.org/150080
old8xp/gyp_from_google,old8xp/gyp_from_google,old8xp/gyp_from_google,old8xp/gyp_from_google,old8xp/gyp_from_google