Refactored @{grep} behavior for improved usability.

Functions in such parcel (e.g., grep_path()) now behave similarly to those in
@{remove} -- which is to say, tolerably sanely. A number of significant
regressions have been documented, if not entirely corrected.

"And so we shamble,
 Whimsical, well-worn, and
 Mesmerically fleet on
 Sodden merry-works and grounded
 Fleets of detritus dreams.

 We, we, and ever we:
 The upstart and classlessly graven,
 Econometrically gimbaled and owned,
 Harbinger-sown and hardly timeless
 Lost generation."