Jenkins-CI Accurev plugin maintenance.

I started working on the Jenkins-CI Accurev SCM Plugin to integrate some additional features that I need for doing automated builds.

from the github pull request for the new features:

I have added two options to the Accurev SCM plugin that I think others may benefit from when using an accurev workspace:

1. there is an option to purge/revert overlaps found in the workspace.
   
   In some accurev scenarios the act of performing a build in a workspace will result in overlaps for subsequent builds. when this happens, the update/populate of the workspace will result in a failed build since accurev will refuse to update a workspace with overlaps. by finding overlaps and purging them prior to attempting to do an accurev update, we no longer fail builds just because of overlaps; and we do not cause the accurev plugin to purge/populate on subsequent builds.
   
   
2. The behavior of purging the workspace on subsequent builds after a build failure occurs is now exposed as an option.
   
   It may be important to not purge a workspace when a build fails. in my case this is important due to the way our config mgmt teams promote code between streams. even though a build fails, I don't want to re-checkout the entire workspace; 99.9% of the time the revert overlaps in conjunction with update in a workspace options will resolve build problems.

I am now working on integrating these new features with some unpublished updates from other folks and trying to bump the SCM API parent version up to something more current. hopefully I'll be able to merge all this together and release an updated plugin in the near future.