Skip flaky tests, with logging

This fixes #2748 (and opens a bunch of other bugs!)
don't try to fix PB on old Twisted versions
Can't use inline conditionals on Python-2.4
replace with statements with explicit patching
work around missing os.errno on py24
replicate any() for python-2.4
Merge branch 'py24-slave-compat' into buildbot-0.8.9

Fixes #2763