[C++-sig] Reworking of indexing suite

[Raoul Gough]

I've made some substantial progress on refactoring the indexing
suite. The new code passes all but one of the existing tests (more
details below). It also splits the proxy facility into a standalone
(C++) container wrapper, and this provides Python-compatible slices in
a wider range of situations. e.g.

  slice = c[1:3]
  c[2].mutate()              # Some change to object
  assert (slice[1] == c[2])  # Slice refers to same object

The one test that it doesn't pass is assigning a single element to a
slice, e.g.:

  c[1:3] = 4

Standard Python lists also don't support this.

All of the new code is in the boost-sandbox cvs under
boost-sandbox/boost/python/suite/indexing and needs a lot of further
testing (in particular, with compilers other than gcc). Any help
and/or comments much appreciated.

-- 
Raoul Gough.
(setq dabbrev-case-fold-search nil)