well, looks like we have to get all the fields right after all --
otherwise problems occur for __SWR mode files. I suppose we could
have lots more flags, but this should be OK.

4.4BSD snapshot (revision 8.1); add 1993 to copyright

trying to get all the fields right is too much trouble: just reset
to a minimal state and let __srefill or __swsetup do the dirty work

rewrite: always allocate buffer immediately; always honor user
mode flags; set fseek optimization iff new buffer is proper size

do early allocation for nonzero size with NULL buffer; cleanup; prettiness

look at size iff buff != NULL; fix from Chris Torek

fflush -> __sflush

new stdio