Improve checkConflict
Improve checkConflict

* Delete temporary RefSpec after checkConflict
* mergeguide use checkconflictInPullRequest instead of checkconflict
(refs #179) Improve merge performance

* merge without tmp dir repository
* remove merging ops from mergeguid
(refs #179) Fetch from fork branch before merge
(refs #179) Remove refs/pull/${issueId}/merge
Merge remote-tracking branch 'master' into improve-pullreq-performance
(refs #179) Refactor
(refs #179) Merge branch 'improve-pullreq-performance'