always run zlib's configure; CFLAGS may have changed

[mr-c]

For @ctb, fixes #442

[mr-c]

• Is it mergable
• Did it pass the tests?
• N/A If it introduces 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 --max-code-length=80
  if needed.
• Is it documented in the Changelog?
• N/A Was spellcheck run on the source code and documentation after changes
  were made?

[mr-c]

Ready for merging @ctb

[ctb]

'make' now always recompiles everything, which is suboptimal... can fix?

[ctb]

Another fix might be to have 'make clean' properly reset things so that configure is run on the next build, no?

[mr-c]

It only recompiles zlib & bzip2; I use ccache and I barely notice a slowdown. I can look into why the 'clean' target is insufficient

[ctb]

On Mon, Jun 09, 2014 at 08:50:48AM -0700, Michael R. Crusoe wrote:

It only recompiles zlib & bzip2; I use ccache and I barely notice a slowdown. I can look into why the 'clean' target is insufficient

please do. Extra compilation steps bug people who work on laptops when
no power is available :)

[mr-c]

distclean is sufficient according to my tests, I redid the PR.

[mr-c]

Merging as it passes the tests and is minimal.