changes in sbcl-1.5.1 relative to sbcl-1.5.0:
* enhancement: restarts for missing package errors.
* optimization: FIND-PACKAGE should be faster even when run in the context
of a package with local package-nicknames.
* optimization: fix TRUNCATE deftransform's results to have well-defined
signs
* bug fix: thread-safety problems in RUN-PROGRAM with :PTY.
* bug fix: SLEEP transform could never fire.
* build enhancement: defend against quirky host floating point
implementation
* test enhancement: allow more parallelism in running the
regression test suite