Use @ticket annotation for tracking related tickets

[duck_]

Instead of using knownWPBug() and related functions I would like to propose using the @ticket annotation for tracking tickets that are related to a test. For example:

/**
 * @ticket 20000
 */

The current patch is a simple demo that supports core tickets only. I was thinking that we would use a prefix or string for other trac's, e.g. @ticket UT102.

(In [891]) Request all open tickets from a Trac install at once.

This prevents repeated HTTP requests for individual tickets and
allows us to keep knownWPBug (or @ticket - see #102) in place for
tickets already closed, without any real performance penalty.
This is good for tracking and also in case a bug is reopened.

This shaved 30 seconds off the test suite run time for me.

(In [893]) Use @ticket annotation for tracking related tickets, largely replacing knownWPBug() and friends.

The existing methods should remain, for use in dynamic or conditional contexts, like the canonical tests or an is_multisite() check.

props duck_. see #102.

(In [894]) Convert knownWPBug and knownUTBug to @ticket annotations. fixes #102.

Allows for an extra description to be included with the annotation,
which will be passed to markTestSkipped().

[896]

(In [984]) Use @ticket annotation in comment.php. see [979]. see #102.