::Conflicts is already unindexed; this adds nothing
avoid weaving pod into ::Conflicts
add dependency on the version that added warning()
avoid inserting filename into warning message

This should be considered a temporary change. I'm only doing this because of
unexpected results on win32, e.g.:
http://www.cpantesters.org/cpan/report/bd5e9b05-6c73-1014-b389-e04455012b15
I'm still trying to figure out what the expected filename should look like,
with respect to forward/back slashes, and what (if anything?) is at fault.
check at build and release time if anything is out of date
v2.021

 - fix incomplete prereq declaration on Test::Warnings
 - work around dubious test failure on win32 with absolute filenames in tests