use system protobuf, potentially fixing bug 471130

(Portage version: 2.2.0_alpha190/cvs/Linux x86_64, signed Manifest commit with key E73C35B3)
Update HOMEPAGE and GIT_SRC for bug #477790.

(Portage version: 2.1.12.2/cvs/Linux x86_64, unsigned Manifest commit)
version bump

(Portage version: 2.2.0_alpha188/cvs/Linux x86_64, signed Manifest commit with key EB9B4AFA)