1171509 - FastForwardXmlFileContext was sometimes using the wrong starting file

BZ: https://bugzilla.redhat.com/show_bug.cgi?id=1171509
Can we move these into a new Pulp 2.5.1 section at the top of this file? Can you also add notes about the bugs that release fixes? While you're in there, would you mind also adding this note from 2.4.4 since this release also addresses that bug:

https://github.com/pulp/pulp/blob/master/docs/user-guide/release-notes/2.4.x.rst#pulp-244