Raise the intraline diff hard limit from 80 to 100 characters

Summary: Fixes T1246. See PHI637. See T13137. Computers have gotten a bit faster so we can probably bump this up a little and see if it causes problems. This is O(N^2) so the this should be less than twice as expensive in the worst case.

Test Plan:
Created a diff affecting characters on a very long line separated by more than 80 but fewer than 100 characters, got a good intraline diff out of it:

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T1246

Differential Revision: https://secure.phabricator.com/D19442