setup and docs: various improvements to setup and docs

setup and docs: various improvements to setup and docs
Remove docs/install-details.html and README.win32 for now (see #282).
Remove checks for pywin32 and pyopenssl in Makefile -- that is (or will be) automated by setuptools.
Remove twisted from setup_requires.  This causes the problem in which Nevow doesn't declare its dependency on Twisted (#440) to yield a clear ImportError mentioning Twisted and to fail repeatedly, rather than yielding a weird ImportError and working on the second identical attempt.
Fix Makefile to set PATH so that trial and twistd can be found by "make test" after Twisted was installed into support/ during "make"