Merge branch 'ab/pcre-v2'

Update "perl-compatible regular expression" support to enable JIT
and also allow linking with the newer PCRE v2 library.

* ab/pcre-v2:
grep: add support for PCRE v2
grep: un-break building with PCRE >= 8.32 without --enable-jit
grep: un-break building with PCRE < 8.20
grep: un-break building with PCRE < 8.32
grep: add support for the PCRE v1 JIT API
log: add -P as a synonym for --perl-regexp
grep: skip pthreads overhead when using one thread
grep: don't redundantly compile throwaway patterns under threading

diff --cc Makefile
Simple merge

diff --cc builtin/grep.c
Simple merge

diff --cc config.mak.uname
Simple merge

diff --cc revision.c
Simple merge

diff --cc t/t4202-log.sh
Simple merge

diff --cc t/test-lib.sh
Simple merge