Merge branch 'rs/grep-p'

* rs/grep-p:
grep: simplify -p output
grep -p: support user defined regular expressions
grep: add option -p/--show-function
grep: handle pre context lines on demand
grep: print context hunk marks between files
grep: move context hunk mark handling into show_line()
userdiff: add xdiff_clear_find_func()

diff --cc builtin-grep.c
Simple merge

diff --cc diff.c
Simple merge