[plt-scheme] 299.15

The v299-tagged code in CVS for MzScheme and MrEd is now version 299.15.

This version reverts changes from 299.14, and we're abandoning the
attempt to constrain program-processing tools (such as Errortrace). The
other half of our security experiment (which is the more important
part) still seems to be working, though. As usual, I'll post a separate
message with details.

Changes:

 * Removed `syntax-recertify-constrained?', 
           `syntax-extend-certificate-env',
           `make-syntax-certificate-env', and 
           `syntax-certificate-env?'.

 * Added `syntax-local-certify', which fits naturally with all of the
   other `syntax-local-' procedures.

 * Changed `syntax-recertify' to move certificates given the
   certificate's inspector or a superior (as opposed to accepting only
   a superior).

 * Added 'module-begin to the set of possible results from
   `syntax-local-context'.

 * Added `begin-with-definitions' to (lib "etc.ss").

 * Changed `eval', `expand', etc. so that only the `module' identifier
   in a `module' form is given context.

   This change avoids problems with using `module' or loading a module
   in a namespace from `module->namespace'.

 * Added `message+check-box' and `message+check-box/custom' to MrEd.
   They're like `message-box' and `message-box/custom', but with an
   extra check box (usually for some variant of "don't ask again").

Temporary docs are in the usual place:

 http://www.cs.utah.edu/~mflatt/tmp/mzscheme-doc.plt
 http://www.cs.utah.edu/~mflatt/tmp/mzlib-doc.plt
 http://www.cs.utah.edu/~mflatt/tmp/mred-doc.plt
 http://www.cs.utah.edu/~mflatt/tmp/insidemz-doc.plt

Matthew