Conduit paste.info method for the pastebin.

Summary:
This implements a paste.info conduit method, for retrieving info about a paste. Imagine that.

Test Plan:
[ricky@rhelpad01 method]$ echo '{"paste_id":1}' | arc call-conduit --conduit-uri=http://phabricator.local/api/ paste.info
{"error":null,"errorMessage":null,"response":{"id":"1","phid":"PHID-PSTE-10934f3df8ed33c06555","authorPHID":"PHID-USER-9d03e8fa47516d37dc92","filePHID":"PHID-FILE-e85f6a72c773d24f4981","title":"test.php","dateCreated":"1307731614"}}

Reviewers:
epriestley

CC:

Differential Revision: 458