Tue Jun 16 11:06:25 CEST 2009

Mfile cleanup

- mfile is now abstract.  it supports conversion into input/output
  port and can be passed to external programs.

- mdir is a hash table of mfiles

- i've included latex.ss as an example.  this code is factored into 2
  parts: command wrappers that call format/system (fsystem) and
  filesystem wrappers that use these together with mfile and mdir

- with-mdir now looks like a let-expression, which resembles its
  semantics.  however it still returns a directory object (external
  programs are mdir->mdir maps) which then can be queried using

(define (tex->dvi tf)
   (with-mdir `(("doc.tex" . ,tf))
              (lambda () (latex "doc.tex")))

- added mfile->bytes and bytes->mfile