GerritTrigger.equals/hashCode -- don't use AbstractProject

AbstractProjects are very temporary and shouldn't be used for
comparison.  Instead, AbstractProject.getFullName() should be
used.

JENKINS-10709: multiple builds are triggered for one change in Gerrit
Merge pull request #77 from docwhat/jenkins-10709-multiple-builds

GerritTrigger.equals/hashCode -- don't use AbstractProject