Rename 'role' file 'role_patch' and remove double definition of ancestor class
Fix core migrations broken by a local patch

The bug is probably on rails side, as ActiveRecord's schema_cache seems
to be stale and Role.reset_column_information hence doesn't work
properly anymore when we have a 'require_dependency "role"'. I don't
know why neither.
Fix Role after_create callback which is broken when running core migrations (e.g. before plugin migrations, when builtin roles are inserted for instance)
Remove useless require (+ broken since my commit commit:0ae9639)
Fix various typos in issue_patch_spec
Refactor issue_patch_spec so things are clearer and examples more concise (still needs some work)
Add missing fixture which otherwise make tests fail if run alone

When running specs only, I had a clean database with no fixture loaded,
and not having "enabled_modules" in this test would make project having
no module hence not allowing viewing issues
(project.allows_to?(:view_issues) returning false)