doc: scheme_reload()

doc: simple-return-primitive?

Changed load/use-compiled: searches for .zo files in
  a "compiled/" subdirectory, and searches for .so/.dll
  files in (build-path "compiled" (system-library-subpath))

system: check for null in string

(let loop ([x 0]) (call/cc loop)) accumulates memory

"synrule.ss" is missing `let-syntax' and `letrec-syntax'

On Alpha machines, floating-point overflow is not handled properly
 (so +inf.0, -inf.0, and +nan.0 are messed up)

Under MacOS, `tcp-listen' does not work reliably

Under MacOS, in the standalone MzScheme application, a blocking read 
 from stdin blocks all MzScheme threads

Under Unix, (execute s) is just (exit (if (system s) 0 -1)), while
 execute* replaces the current process like it is supposed to

Under Windows, the `system' procedure blocks all MzScheme threads
 (`system*' works correctly)

Under AIX, write to tcp output port blocks when the low-level
  buffer is full

Under FreeBSD, if the descripters limit is greater than 256, then
  it is automatically reduced to 256 within MzScheme/MrEd/DrScheme

Still to be added to support R5RS:
  (scheme-report-environment n)
  (null-environment)
  (interaction-environment)