Modified Authorization Grant to accept a GET with parameters in the Query String

The RFC Spec for OAuth 2 specifies that the Authorization Grant endpoint be a HTTP GET.  POST is allowed
to be supported, but GET must be implemented according to the spec.  This change modifies authCodeGrant.js
to look for the appropriate parameters in either the query string or the body, so HTTP GET and HTTP POST
are both supported.

Added tests to test/authCodeGrant.js to test both POST and GET functionality.
Merge upstream changes
Merge branch 'master' of github.com:thomseddon/node-oauth2-server
Added an option to require client credentials either in the body or in the Auth Header for AuthCodeGrants.  This is set via a config flag "requireAuthGrantCredentials".  If this flag is true, then a clientId and a clientSecret is required via either the authHeader or the body (if a post).    The flag defaults to false to maintain backwards compatibility.
Added option to pass client secret in either body, query string, or auth header
Merge pull request #73 from mjsalinger/authGrantCredentials

Auth grant credentials