util.h: declare dirstateTupleType variable instead of defining it
The definition is already in parsers.c
This patch avoids, at least on Mac OS X 10.6.8, build issue since
e250b8300e6e
test-context: add test for performing a diff on a memctx
We now see the first result of all that refactoring of memctx: we can now diff
against a memctx.