twisted.internet.test.reactormixins.ReactorBuilder.unbuildReactor uses many non-interface APIs of reactors

[exarkun]

_uninstallHandler and disconnectAll are part of no interface, but ReactorBuilder tries to use them to clean up a reactor it just ran. It also uses getDelayedCalls without checking whether the reactor implements IReactorTime.

These uses lead to problems testing reactors that are missing one or more of these APIs.

[exarkun]

Attached a patch that makes these optional using a getattr trick, similar to one that's there already.

Of course, ultimately the real fix is to have reactors know how to clean up after themselves.