grep: add option -p/--show-function
The new option -p instructs git grep to print the previous function
definition as a context line, similar to diff -p. Such context lines
are marked with an equal sign instead of a dash. This option
complements the existing context options -A, -B, -C.
Function definitions are detected using the same heuristic that diff
uses. User defined regular expressions are not supported, yet.
Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <gitster@pobox.com>