ENH: allow binstar user to configure verify

The user must do :

    binstar  config --set verify [True|False|/path/to/rootCA.pem]
    -or-
    binstar  config --set sites.siteName.verify [True|False|/path/to/rootCA.pem]
Changed name of verify to verify_ssl
DOC: added better config help
FIX: updated docs and command