Improved(?) package name parsing

[dalehenrich]

@ThierryGoubier published the following for Pharo-6.0: https://github.com/dalehenrich/filetree/issues/201#issuecomment-242765843. The original issue has to do with the fact that Monticello does not allow two packages to share a common Prefix: 'AAA' and 'AAA-BBB' are not allowed to co-exist in an image ... In Pharo5.0 at some unknown point in time, Pharo began allowing packages named 'AAA' and 'AAA-BBB' to exist ....

Anyway, the issues with 'AAA' and 'AAA-BBB' related to the calculation of package membership based on pattern matching in class categories and method protocol are not really relevant here, except for the fact that @ThierryGoubier patch might actually be addressing some other issue and I'm dropping off the issue to see if the Squeak and GemStone variants need patching as well ...