Mongodb devel 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.
Can be any length as long as the hash is unique (if it's not the URL will 404). Normally 6-8 is enough.