Clean up test state in the `FilePath` tests on Windows so that `_trial_temp` can be deleted

Author: mhaarhaus
Reviewer: tom.prince, itamar, exarkun
Fixes: #5228

Previously a `FilePath` test left some files in `_trial_temp` without permissions
necessary to delete them.  This made clean up _trial_temp a pain.  The test now
makes sure to restore permissions on the dummy files after the test is over.


git-svn-id: svn://svn.twistedmatrix.com/svn/Twisted/trunk@38294 bbbe8e31-12d6-0310-92fd-ac37d47ddeeb
Merge ssl-chain-cert-2061

Author: hynek
Reviewer: exarkun, tom.prince
Fixes: #2061

Add support for certificate chains to `twisted.internet.ssl.CertificateOptions`.


git-svn-id: svn://svn.twistedmatrix.com/svn/Twisted/trunk@38305 bbbe8e31-12d6-0310-92fd-ac37d47ddeeb
Merge ssl-largewrite-throughput-6477

Author: exarkun
Reviewer: therve
Fixes: #6477

In `twisted.protocols.tls`, replace some O(N**2) complexity buffer handling
code with some code of somewhat lower complexity.  This primarily helps
improve performance when a single call to `write` is passed a very large
string (the further above 2 ** 16, the bigger impact this will likely
have).


git-svn-id: svn://svn.twistedmatrix.com/svn/Twisted/trunk@38313 bbbe8e31-12d6-0310-92fd-ac37d47ddeeb
Apply 6444v3.patch: Improvments to the test_usage docstrings

Author: stephsolis
Reviewer: rwall
Fixes: #6444

Improvments to the test_usage docstrings.



git-svn-id: svn://svn.twistedmatrix.com/svn/Twisted/trunk@38347 bbbe8e31-12d6-0310-92fd-ac37d47ddeeb
twisted.web: replace calls to string module's function to string method

Fixes: #5004
Remove unused imports
Improve test coverage for twisted.web.twcgi.CGIScript's render method
Improve test coverage of twisted.web.util.htmlIndent
Cosmetic on test names