Adding a switch that allows mocked requests to be properly prepared by LWP, so that default headers are included in mocked requests
Make get et al. work on global $mock_ua object

Previously this would cause a warning like 'get is not mocked'
 add Andreas König and Ash Berlin to acknowledgements
Merge branch 'antipasta.default_headers_broken' of https://github.com/antipasta/Test-Mock-LWP-Dispatch
 DEFAULT_REQUEST_HEADERS = 1 by default
 add Joe Papperello to acknowledgements