New restriction is added to MANAGE_PROPOSAL_ACCESS_CHECKER.

Organization admins or mentors should not be able to modify the proposal after
accepted students are announced.

We also discussed that there should be a cut off date earlier, i.e. before
students are actually announced, after which no modifications are permitted
so that organanization admin cannot game the system and, for example, play
with duplicates. But we do not need this extra logic because it has never been
a real problem. And organization admins is a relatively trusted group.

BUG=https://code.google.com/p/soc/issues/detail?id=2635

Change-Id: I5b51b732849402f00feb8379df4db56978cb0a62
1 file changed