(stable) Fix two issues with repository monogram regular expressions

Summary: Ref T4245. Fixes T10172. These regular expressions were simply incorrect: they intend <start> (form one | form two) <end> but were written as (<start> form one) | (form two <end>) which allowed stuff like "R2/R13" to be interpreted as a monogram because it matches (<start> form one).

Test Plan: Parsed commit ba46ffa6169c from RTEMS repository, see T10172. Before patch, got an identical trace; after patch, clean import.

Reviewers: chad, avivey

Reviewed By: avivey

Maniphest Tasks: T4245, T10172

Differential Revision: https://secure.phabricator.com/D15049