Integrate with new core SVN-develop PHPUnit Setup

[ericlewis]

The new WordPress SVN-develop setup now includes phpunit within the repository. This means for our development environment, we could use just this single repo, along with a BuddyPress svn repo checked out within the plugins folder, and integrate the two.

There's some assumptions made within the current tests setup code that don't allow us to do this easily though. Let's fix that.

[ericlewis]

attachment:5200.diff​ offers support for using the new develop svn environment single-handedly, while also providing backwards compatibility for users referencing an explicit location for the WP PHP unit folder location.

[boonebgorges]

Teh hotness

[boonebgorges]

One thing - could you make it so that things die more gracefully if both attempts at setting WP_TESTS_DIR fail? In other words, file_exists( WP_TESTS_CONFIG_PATH ) > die( 'whatevs' )

[ericlewis]

totally

[boonebgorges]

In 7421:

Improve compatibility with develop.svn.wordpress.org unit test suite

This changeset ensures that the BP tests can be run from within a
develop.svn.wordpress.org setup. Backward compatibility for custom locations
using the WP_TESTS_DIR environment variable is maintained.

Fixes #5200

[boonebgorges]

In 7424:

Better backward compatibility for tests configuration

Improved support for the old WP_TESTS_DIR environment variable, in particular
when pointing this environment variable toward the new develop.svn.wordpress.org
configuration.

See #5200