remove _markerlib from manifest

Signed-off-by: Gabi Davar <grizzly.nyo@gmail.com>

Update rationale for the zip_safe flag

Importing from a zip file no longer significantly reduces the number
of stat calls during import, and may even slow imports down if
too many archives are added to sys.path.

The outdated rationale was noted by Thomas Güttler on distutils-sig

Swap out hard tabs for spaces

Instead of reasing a new exception, just augment the existing exception, avoiding any concerns about exception type, but still communicating the context necessary to trace the issue. Ref #537.

This helps finding packages with bad utf

Stop comparing repr()'s in TestEntryPoint

Adjust expectation that 'extra' is not in the marker evaluation if no extras demanded the requirement.

Reinstate the or guard in WorkingSet._markers_pass

Checking hundreds of possibly installed packages manually should NOT be expected of the user ;)

In Python 3, the default order of iterables can not determined,
so comparing the repr of objects that include tuples is not static
like it is under Python 2. Compare the attributes of EntryPoint
instead, making sure to sort .attrs and .extras.

Closes: #526

Restore evaluating environment markers in WorkingSet

Correctly deal with parsed requirements that include extras as a
marker inside WorkingSet that are populated from METADATA inside
wheels, like we get from pip>=7.

This partially reverts commit 04d10ff0.

Closes: #523

Drop unused safe_repr function

When _assertIn was removed from test_resources, the safe_repr
function was not dropped, leaving it with no callers, so drop it.