adds options for client certs to downloader class

Adds :client_cert to the env array and then passes it into the curl
options array
adds param for client certs

adds an option to the command parser for client certicates
adds client cert
adds client cert to default config
adds accessor for client_cert
passes client cert option from Vagrant file to box_add
Merge branch 'master' into client-certs
implemetn array arguments from #1569
check ENV for VAGRANT_NOCOLOR (equivalent of --no-color on cmdline)
Ansible: Improvements for 'extra_vars' argument

`extra_vars` argument can now:
- contains a hierarchical set of parameters (instead of flat Key-Value Pairs)
- alternatively refers to a configuration file (instead of embedded Hash)

See Ansible Documentation for version requirement details:
http://www.ansibleworks.com/docs/playbooks_variables.html#passing-variables-on-the-command-line
Allow owner & group to be supplied as an Integer and skip lookup
Restore correct pathing
fix nfs mount fail with freebsd.
Sleep to avoid 100% CPU in waiting time of 'vagrant up'
Add --no-parallel to provision
Merge pull request #2401 from txchen/master

core: sleep to avoid 100% CPU in waiting time of 'vagrant up'
Update cHANGELOG
.vimrc with vagrant tabstop settings

Signed-off-by: BlackEagle <ike.devolder@gmail.com>
document common validation pattern
Automatically enable symlinks on vboxsf for VirtualBox 4.1 (see #713 and 387692f9c8fa4031050646e2773b3d2d9b2c994e).