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

Also made link to detailed doc instructions more prominent
move zlib & bzip2 to third-party
sloccount for humans and Jenkins
remaining changes to support third-party/
Merge pull request #427 from ged-lab/feature/sloccount

sloccount Makefile target
Move Coverity scan to Makefile; simplify jenkins-build.sh