#7 Ultimate fix for bug 989547

[Stephen Clouse]

Well, 2.027 is still broken with tarfiles that are for
whatever reason missing a trailing slash on the initial
directory name. I'm not even sure how someone manages
to DO this, but it apparently needs to be accomodated.
Module::Signature is one broken module I stumbled on.

Anyway, this reapproaches the problem by looking for
(Makefile|Build).PL in the file list, which (I believe)
is guaranteed to be in the top level directory, and
then just stripping the filename off. No worrying
about trailing slashes.

[Stephen Clouse]