Fix #1454 by requiring package.el eagerly

Just adding "(require 'package)" to "el-get-elpa-package-directory"
fixes this bug, because by the time any elpa package is being installed
or fetched, package.el has to be available, so all we have to do is load
it if it hasn't already been loaded.

The fix is in 99cb036. The test is in b9ae825. 40970c4 contains a semi-related improvement to package.rcp.