Take cpp-common branch with cURL fixes
Point at fixed master version
Merge pull request #419 from Metaswitch/curl_fixes

[No review required] cURL fixes
Enhance fakecurl to cope with the resetting of cURL options
Fix for consistent NULL checking
Merge pull request #420 from Metaswitch/curl_fixes

[Reviewer: Ellie] Enhance fakecurl to cope with the resetting of cURL options