[plt-scheme] 301.11

MzScheme and MrEd are now version 301.11 in the SVN repository trunk.

(Version 301.10 never made it out of my development branch.)

IMPORTANT: since the new `compiler-enforce-module-constants' parameter
defaults to #t, module re-definition is effectively prohibited by
default. Also, in a namespace produced by `module->namespace', a
variable can't be redefined or `set!'ed unless the original module
`set!'ed the variable (or the variable wasn't defined at all). If you
use `module->namespace' and/or module re-definition for debugging, then
set `compiler-enforce-module-constants' to #f.

Changes:

 * The bytecode compiler now inlines some functions bound by `let',
   `letrec', or a module-level `define'. The conditions for inlining
   are typical (e.g., the function has to be "small"). Currently,
   module-level definitions are inlined only within the same module.

 * By default, a variable defined in a module top-level is immutable,
   unless the module (in expanded form) contains a `set!' on the
   variable.

   The only way to `set!' such variables before was to use
   `module->namespace', or to redefine the module. Now, those don't
   work either, unless the `compiler-enforce-module-constants'
   parameter is set to #f before compiling the module.

   If `compiler-enforce-module-constants' is set to #f, then module
   bindings are not inlined, and the JIT must generate certain run-time
   checks that are otherwise unnecessary.

 * Changed `file-position' so that eof as a second argument moves to
   the end of a file/string port.

 * Added `procedure-closure-contents-eq?', which is useful for certain
   caching operations (e.g., in the implementation of lazy contracts).

Matthew