Support the modern METADATA file in extension packages.

Review Request #8068 — Created March 21, 2016 and submitted — Latest diff uploaded

Information

Djblets
release-0.8.x
4329741...

Reviewers

Modern Python packages store metadata in a METADATA file, rather than in
a PKG-INFO file. This updates our extension metadata parsing to try this
file first, falling back on PKG-INFO. That gives us compatibility with
any modern packages (particularly wheels), while retaining support for
older packages (eggs).

Tested this with an extension containing a METADATA file but not PKG-INFO.
Successfully extracted metadata from the package for the extension.