This reduces the risk of leaving a corrupted .installed.cfg

Version string is now N.N.N.postN to follow http://legacy.python.org/dev/peps/pep-0440/ .
(Ideally it should be N.N.N+SlapOSNNN, but version string containing '+' sign does now work
with older setuptools, that can be still used at the very beginning of bootstrap process.)

Conflicts:
	.gitignore
	setup.py
	src/zc/buildout/buildout.py
	src/zc/buildout/download.py
	src/zc/buildout/easy_install.py
	src/zc/buildout/testing.py
	src/zc/buildout/tests.py

Add referred parts' hash strings in __buildout_signature__, that invokes rebuild of a part when one of its (recursive) dependencies are modified.

Also remove duplicates and sort entries in __buildout_signature__.

       buildout-2-compatible recipes weren't expressed correctly,
       leading to unintendional use of zc.recipe.egg-2.0.0a3.

can't release them to pypi anymore.

zc.recipe.testrunner past version 1

itself past version 1.

Versions in versions sections can now be simple constraints, like
<2.0dev in addition to being simple versions.