This directory is for 3rd party code we pull in.  Principally intended
for small util-ish functions, or possibly optionally-built  local
implementations of common-but-not-universal library functions.  Each file
should include information about its source and licensing.  Unless
otherwise specified, that information in the file is complete;
specifically, none of them automatically inherit from the base COPYRIGHT
file.

These are kept in a separate dir both for easy identification, and to
move them out of the way of 'make indent', since we generally want them
kept as closely as possible in sync with their upstreams.