COMPAT: dateutil 2.5.0 bug fix
COMPAT: test with latest dateutil via pip
COMPAT: dateutil 2.5.0 bugfix causes some tests to fail, skip for now

xref #12611

cc @neirbowj 

maybe we should just raise on this version, this is a very subtle bug which they should have tested (and which used to work). If they put out a fix before next release of pandas then I think we will. 
