IdentiesOnly will not disable ssh_agent as it's not supposed to, a new option :use_agent provided for disabling agent. Fix #148 with another fix for #137.
Fixed typo user agent was writen instead of ssh-agent
Merge pull request #159 from mfazekas/281_ssh_config_fix_for_public_key_auth

IdentiesOnly will not disable ssh_agent as it's not supposed to - fixing #148 by new fix for #137