Skip thread tests under Devel::Cover
Rewrite writiability test to be clearer and with less warnings
Yet another attempt to solve the mystery-win32-failure cpantesters report

While fa19e5d6 was a nice idea, its test was flawed. As seen in the fresh fail
http://www.cpantesters.org/cpan/report/137dfaf3-7bbc-1014-aec2-3d202b825c07
the writability test passed with flying colors, but the lock didn't open right
after that. The only explanation at this point is that the FS underlying this
particular dir can not create filenames starting with a dot <facepalm />
Alternatively it may have to do with the umask(0) call, but this seems even
more insane.

Thus (as unlikely as it seems) the culprit seems to be the name. Hopefully
changing it will be the end of this and we will smoke happily ever after...
Skip annoyingly failing test on broken base.pm

Was broken in 5.19.7, fixed in 5.19.8
Make 54taint.t actually test the DBIx::Class in lib (originally 689e22d1)
One extra cleanup pass before asserting weakregistry is empty
Factor out the symtable walker, no functional changes but much reshuffling