Merge branch 'ab/grep-patterntype'

Merge branch 'ab/grep-patterntype'

Some code clean-up in the "git grep" machinery.

* ab/grep-patterntype:
  grep: simplify config parsing and option parsing
  grep.c: do "if (bool && memchr())" not "if (memchr() && bool)"
  grep.h: make "grep_opt.pattern_type_option" use its enum
  grep API: call grep_config() after grep_init()
  grep.c: don't pass along NULL callback value
  built-ins: trust the "prefix" from run_builtin()
  grep tests: add missing "grep.patternType" config tests
  grep tests: create a helper function for "BRE" or "ERE"
  log tests: check if grep_config() is called by "log"-like cmds
  grep.h: remove unused "regex_t regexp" from grep_opt