Introduced contrib/eproject-find-cmd.el

Combine find-cmd with eproject to define your eproject files, an
alternative to :relevant-files, to avoid building very long shell
command strings.
Work around for find-cmd results having absolute path results.

find-cmd tries to put (expand-file-name default-directory) on the command line,
but that results in find-grep output having long absolute pathname matches (and
pushing interesting info off the right margin).  This forces a find-cmd always
rooted at '.', which will be (eproject-root).