Bug 1082447, bump limit for gpg signing to 750MB, r=mgerva
Merge default --> production
bbbug 1082685: migrate one 10.6 mac signing machine to 10.9 - remove mac-signing4 from active duty. r=callek
Merge from default.
Bug 1008052, turn down concurrency on mac signing servers, r=bustage
Merge default  -->  production
Bug 1081313: add Yosemite packages; r=simone

This installs XCode (seed) on Yosemite and upgrades the build scripts
for Python, Mercurial, and Wget.  Working around some Yosemite bugs in
the process.
Merge default -> production