Here is the next version, it feels very close to finished. As before, I
haven't ran a bootstrap or the full testsuite yet but I did run the
explicit-obj tests which completed as expected.

There's a few test cases that still need to be written but more tests
can always be added. The behavior added by CWG2789 works in at least
one case, but I have not added tests for it yet. The test cases for
dependent lambda expressions need to be fleshed out more, but a few
temporary ones are included to demonstrate that they do work and that
the crash is fixed. Explicit object conversion functions work, but I
need to add fleshed out tests for them, explicit-obj-basic5.C has that
test.

I'll start the tests now and report back if anything fails, I'm
confident everything will be fine though.

Alex