Detect the snapshot version number using darcs
For non-release builds, we want to append a date to the version number (e.g. 6.7.20070206). Previously this was done by the nightly build script, this new method figures out the snapshot version by querying the darcs repository and finding the date of the most recent patch (actually it finds the most recent of the last 100 patches, but that should be good enough). This is done by the configure script. To handle source distributions, we create a file VERSION in the top-level directory that contains the version number, and ship this in the source distribution. The configure script picks up the version from this file if it doesn't see a _darcs directory.