Exclude `oauth_callback` with :exclude_callback
Exclude `oauth_callback` with :exclude_callback

When working with partially compliant 1.0 Service Providers, the
`oauth_callback` parameter can be omitted from the request token
phase with the `:exclude_callback` request option.

felixbuenemann/oauth-ruby,ministrycentered/oauth-ruby,guimello/oauth-ruby,JonathonMA/oauth-ruby,mrThe/oauth-ruby,gherry/oauth-ruby,galois17/oauth-ruby,pelle/oauth,mkrisher/oauth-ruby