gson 2.3 has internal bug that it doesn't work with some versions of maven.

gson 2.3 has internal bug that it doesn't work with some versions of maven.

This change makes use of new imports attribute for Bazel's Python rules, which
enable adding directories to the PYTHONPATH. This allows us to remove
the hack for building protobuf's Python support with Bazel and now
allows projects to include protobuf using a Bazel external repository
rather than requiring it to be imported directly into the source tree as
//google/protobuf.

This change also updates the protobuf BUILD file to use a named
repository, @python//, for including Python headers rather than
//util/python. This allows projects to specify their own package for
Python headers when including protobuf with an external repository.

Fixes #1230

--strip_prefix doesn't seem to work.

Change-Id: I63ed5fb58a45e098f2fd1fa457a219148de030bd

Change-Id: I5a299d969ff96d7d2f80aadc7e8987d461d24b8f

committer: Jon Skeet <skeet@pobox.com>