Issue #18103: Update README.txt and test_idle to describe and run gui tests.
#18155: Regex-escape delimiter, in case it is a regex special char.

Patch by Vajrasky Kok, with slight modification to the tests by me.
Tempfile.py: stop buildbot warning about using deprecated xreadlines.

The slightly odd behavior (the validity of passing a sizehint depends on the
type of self._file) was kept to avoid breaking code that depends on it.
Test_tempfile.test_xreadlines passes (along with everything else).
Issue 18189: remove unused methods in idlelib.Delegator.Delegator.
Idle code already uses x.delegate instead of x.getdelegate().
The printed report must have been for testing.