nightlybuilds: switch to git.
Also specify branch to test to startnightly
nightlybuilds: use '-f' with 'git clean'
git change: update PETSC_VERSION_GIT in version.c [to be in sync with petscversion.h]
git change: update configure to remove auto-cloning of BuildSystem
git change: update configure to support 'git' detection and git 'clone' detection
nightlybuilds: update builddist to also take 'branch' as option.
If (branch=master) build petsc-dev.tar.gz else build petsc-BRANCHNAME.tar.gz
Also git clean need -d to remove dirs.
nightlybuilds - update git commands - and use 'petsc.clone' as reponame
nightlybuilds: also clean gitignores (build products)
Merge branch 'balay/nightlybuilds-change-to-git'

* balay/nightlybuilds-change-to-git:
  nightlybuilds: also clean gitignores (build products)
  nightlybuilds - update git commands - and use 'petsc.clone' as reponame
  nightlybuilds: update builddist to also take 'branch' as option. If (branch=master) build petsc-dev.tar.gz else build petsc-BRANCHNAME.tar.gz Also git clean need -d to remove dirs.
  git change: update configure to support 'git' detection and git 'clone' detection
  git change: update configure to remove auto-cloning of BuildSystem
  git change: update PETSC_VERSION_GIT in version.c [to be in sync with petscversion.h]
  nightlybuilds: use '-f' with 'git clean'
  nightlybuilds: switch to git. Also specify branch to test to startnightly