Update to Racket 5.1.1

Changes in version 5.1.1, May 2011:

Enabled single-precision floats by default
Added single-flonum?
Changed eqv? so that inexacts are equivalent only when they
have the same precision
Changed file-or-directory-permission to add 'bits mode
and permission-setting mode
Added special treatment of void as an 'inferred-name property
Removed the "MrEd" compatability executable under Windows
and Mac OS X, but the "mred" compatibility script remains
racket/gui: added multi-column support to list-box%
racket/gui: added scrollbar support to panel%, vertical-panel%,
and horizontal-panel%
racket/gui: added 'wheel-left and 'wheel-right events
racket/file: add user-read-bit, etc.
racket/contract: removed some (undocumented) exports.

Changes in version 5.1, February 2011

Renamed "proxy" to "impersonator"
Added current-get-interaction-input-port, which enables
racket/gui events to be dispatched while a REPL is blocked
Changed equal? to equate C pointers when they refer to the
same address
Internal: weak boxes are cleared before non-will-like
finalizers; use late-weak boxes to get the old behavior

Changes in version 5.0.2, October 2010

Changed body of `when', `unless', `cond' clauses, `case'
clauses, and `match' clauses to be internal-definition contexts
Swapped unsafe-vector*-ref with unsafe-vector-ref, etc.
Added ->i to the contract library, improved ->*, adding #:pre and
#:post, as well as making the optional arguments clause optional.
Added #true and #false, and changed #t/#T and #f/#F to
require a delimiter afterward
Added print-boolean-long-form
Added read-accept-lang, which is set to #t when
reading a module
Added flonum?
Changed continuation-marks to accept a #f argument
to produce an empty set of marks
Added fxvectors
Added unsafe-{s,u}16-{ref,set!}
Added prop:proxy-of
Added proxies to go with chaperones, and renamed chaperone property
as proxy property; beware that the word "proxy" will change in
a future version, perhaps to "impersonator"
Added collection-file-path and collection splicing at the file
level

(asau)