cosmetic change

switch epoll from level triggering to edge triggering

Noted by Matthew Dempsky
  open_* from open.h now open in large file mode

example, you can say that fmt_quotedprintable should also escape ':', if
you want to use ':' as separator in a data file.

document that the iob_write callback should limit itself

also add compat formatting routines that will output v4-mapped addresses
  as ipv4 addresses

scan_ip6 returned 1 for "::"

byte_rchr did not work at all (oops)
uudecode now handles yenc (a little)

byte_copy and add buffer_putspace, a trivial shortcut.