fix vim modeline
test ourselves again, by running a standard t/00-check-deps.t test
prove -lr t is no good here - we need a META.*
failing tests show the file and line as the .t, not us

This also allows the caller to be able to set $TODO and have it properly
detected by Test::Builder.
Merge pull request #6 from Leont/topic/tb_level

Set Test::Builder::Level correctly

Also add an additional selftest and add a diagnostic against prove.