Update Jenkins build status badge
Fix link to virtualenv installation instructions.

Also made link to detailed doc instructions more prominent
Merge pull request #427 from ged-lab/feature/sloccount

sloccount Makefile target
move zlib & bzip2 to third-party
sloccount for humans and Jenkins
remaining changes to support third-party/
pip -> pip2 fix
Merge branch 'accaldwell-master'
Move Coverity scan to Makefile; simplify jenkins-build.sh
Merge pull request #421 from ged-lab/feature/simplify-jenkins-build

Move Coverity scan to Makefile; simplify jenkins-build.sh
don't run half the coverage checking if we can't run it all
support using system zlib or bz2, or both