Rgrep is a clone of the SLang-based rgrep that ships with the `jed`
text editor.   It was written when I tried to port the SLang editor to a
modern Linux distribution and was thwarted because the pre-packaged copies
of the library were not complete enough to actually run the program.

Rgrep implements most of the functionality of the reference program,
lacking only {min,max} and \d in the regular expression language and the
long options --version and --help.  It uses Henry Spencer's BSD-regex
library (slightly modified to more closely resemble the SLang regular
expression language) to provide a slow, but functional, recursive grep.