[Ur] New release

[Adam Chlipala]

Available as usual at: http://www.impredicative.com/ur/

CHANGELOG for this release:

- Changes to encoding of SQL aggregate functions: nullable types may be
   aggregated, and non-COUNT aggregates return nullable results.
- SQL subqueries may apply aggregate functions to columns bound in enclosing
   queries.
- Switch from libmhash to OpenSSL.
- 'cdataChar', for injecting arbitrary character codes into XML
- 'crypt', for access to the standard UNIX password encryption routine
- 'readUtc', for parsing time strings in the UTC time zone
- Built-in 'time' type now stores microseconds (which for now are only 
used in
   connection with Postgres timestamps).
- Client-side URL blessing and redirection
- 'currentUrlHasPost' function
- Transactional 'free' functions now passed an argument indicating 
whether the
   runtime system expects to retry the transaction.
- Change tasks to allow task kind-specific inputs
- Add 'clientLeaves' and 'periodic' task kinds
- Support for externally-callable pages, via the 'postBody' and 
'queryString'
   types and the 'effectfulUrl' function
- 'minHeap' and 'alwaysInline' .urp options
- '-prefix' command-line option
- Comments in .urp files (lines starting with '#')
- Miscellaneous additions to the standard library
- Bug fixes and improvements to type inference and optimization