Mongodb: 2.7.7

Closes #32886.

The level of patching here is getting a little silly. Mongo are currently shifting around a fair bit of their codebase, and that is currently causing the HEAD build to fail.

The devel build also needs patching, discussed [here](https://jira.mongodb.org/browse/SERVER-15555), but that fix has been merged into the HEAD and consequently is scoped to only the devel build.

The last patch is the SConstruct file to accept 10.10 as a valid build option on Yosemite, which is in neither stable, devel or HEAD currently.