Revert accidental deletion of package-built-in-p

This partially reverts commit 300dbb1e183afd63721ee4e83e105e494b83d8d7.

Conflicts:
	lisp/ChangeLog
Typo
(package-list-loaded-files) A couple of symbol refactorings

Rename path to file and package-list-loaded-files to
package--list-loaded-files
(package--list-loaded-files) Return a recursive list of files