As suggested on the list, this splits the cairo-boilerplate-glitz.c
file in three separate files, one for each backend. Furthermore,
it fixes a few problems in compilation of the AGL backend test harness.
A new meta-surface backend for serialising drawing operations to a
CairoScript file. The principal use (as currently envisaged) is to provide
a round-trip testing mechanism for CairoScript - i.e. we can generate
script files for every test in the suite and check that we can replay them
with perfect fidelity. (Obviously this does not provide complete coverage
of CairoScript's syntax, but should give reasonable coverage over the
operators.)