support using system z,bz2 libraries

[mr-c]

The default is to use the bundled libraries.

To use the system zlib and bzip2 change setup.cfg or use the --libraries z,bz2 parameter which will make our
custom build_ext command strip out the bundled versions.

[ged-jenkins]

Test FAILed.
Refer to this link for build results: http://ci.ged.msu.edu/job/khmer-multi-pullrequest/344/

[mr-c]

Hmm.. cppcheck found new code warnings (otherwise the build passed).

This will close #334

[ged-jenkins]

Test FAILed.
Refer to this link for build results: http://ci.ged.msu.edu/job/khmer-multi-pullrequest/346/

[mr-c]

test this please

[ged-jenkins]

Test PASSed.
Refer to this link for build results: http://ci.ged.msu.edu/job/khmer-multi-pullrequest/360/

[mr-c]

• Is it mergable
• Did it pass the tests?
• N/A If it introduce new functionality in scripts/ is it tested?
  Check for code coverage.
• Is it well formatted? Look at pep8/pylint, cppcheck, and
  make doc output. Use autopep8 and astyle -A10 if needed.
• Is it documented in the Changelog?