Prevent a NPE in intializer

wait for descriptor to be loaded so initializer can get it.
GetPrivateKeys unnecessary if BasicSSHUserPrivateKey works correctly to begin with.
1.10 released, can use it now.
Include jgit http server jar in git-client-plugin for API consumers

[JENKINS-21756] shows that JGit version mismatches can complicate the
management of plugins. Including JGit http server in this plugin is
hoped to reduce the version mismatch cases.
Update to 1.11.0-SNAPSHOT, larger changes justify the switch

Updating to JGit 3.5.1, dependencies on newer versions of other
plugins, etc.
[maven-release-plugin] prepare release git-client-1.11.0
[maven-release-plugin] prepare for next development iteration
Merge remote-tracking branch 'upstream/master' into proto-jdk8

Conflicts:
	src/main/java/hudson/plugins/git/GitTool.java