Summary:
Previously we would have to decompress the entire manifest to check if each
sparse profile existed. This slowed hg status down by 500ms (2x).
This patch adds caching when simplecache is enabled.
Test Plan:
Added a test. Also tried it in fbsource. Verified repeated hg
status's did not parse the manifest
Reviewers: rmcelroy, ericsumner, lcharignon, akushner, mitrandir
Differential Revision: https://phabricator.fb.com/D2158178