[plt-scheme] Automatic compilation for drscheme's Module language

[ The below is not in the upcoming 4.2.1 release, but will be in the
one after. ]

A few minor organs in DrScheme's Module language's intestines have
been rearranged [1] with the overall change that hitting "Run" while
in the module language should both be faster and have less stacktrace
information, i.e., per-function instead of per-subexpression (which
should still be plenty for most purposes).

The speedup comes from two changes: DrScheme now keeps up to date .zo
files in compiled/ directories whenever a program is run and the
errortrace library is not being used anymore (by default). To keep it
from being too fast, tho, DrScheme instructs the JIT not to perform
function inlining, with the additional benefit that the stacktraces
should match what you'd expect [3] by looking at the program text.

All of this can be changed (to bring back the old behavior) in the new
details section of the language dialog.

Robby

[1] Yes, exactly like that: http://wiki.lspace.org/wiki/Swamp_dragon
[2] For now, use Eli's profiler instead of DrScheme's anyways.
Hopefully DrScheme will change at some point to use it too.
[3] Assuming you expect that tail calls won't show up.