[plt-scheme] 299.18

The exp-tagged code in CVS for MzScheme and MrEd is now version 299.18.

Changes:

 * Changed permissive UTF-8 decoding to include a "?" for every
   ill-formed byte, instead of just those bytes with high bits. This
   means that tracking positions in a port is slightly more expensive,
   but it's consistent with most other applications.

 * Changed the random-number generator to use L'Ecuyer's MRG32k3a
   algorithm, as encouraged by SRFI-37.

   Changed `random' to accept 0 arguments, in which case it generates
   an inexact number between 0 and 1, exclusive.

   Added `pseudo-random-generator->vector' and
   `vector->pseudo-random-generator'.

 * Changed `{read,peek}-bytes-avail!{,*,/enable-break}' to produce a
   special-reading procedure when an input port produces a special.

 * Added `syntax-property-symbol-keys'.

 * Added `make-pipe-with-specials' to MzLib's "port.ss"; procedures
   like `copy-port' now also handle specials.

 * Extended result of `syntax-local-certifier' (see docs).

Matthew