[Ur] PATCH: -version flags for urweb compiler

[Adam Chlipala]

austin seipp wrote:
> The compiler has never had a version flag, so attached is a patch that
> adds some support for build/compiler versions.
>    

Thanks!  I've pushed a changeset based on yours, but with a different 
versioning scheme.  I'm including the latest release number in 
configure.ac, along with code that, if this is marked as a 
$WORKING_VERSION, queries 'hg identify' to get extra information to 
append afterward.