Support for request signing via ssh-agent
Fixes for tags for pre7 api, more ssh-agent improvements Refs: kevinykchan/knife-joyent#37
Merge remote-tracking branch 'fog/master' into ssh-agent

Conflicts:
	lib/fog/joyent/compute.rb
Merge pull request #1854 from kevinykchan/ssh-agent

[joyent|compute] support for http-signature-auth using ssh-agent -- Closes #1854