incremental-repack: do not repack files over a configuration based size
Incrementally repacking too big files results in more problems than
solving them like the repack taking a long time to finish and eventually
culminating in a one huge pack file. Therefore, it is preferable to ignore
files over a certain size during the incremental repack.
Test Plan: Added a test and ran all the tests.
Reviewers: #fbhgext, durham
Reviewed By: #fbhgext, durham
Differential Revision: https://phab.mercurial-scm.org/D1588