log --grep: accept --basic-regexp and --perl-regexp

When we added the "--perl-regexp" option (or "-P") to "git grep", we
should have done the same for the commands in the "git log" family,
but somehow we forgot to do so.  This corrects it, but we will
reserve the short-and-sweet "-P" option for something else for now.

Also introduce the "--basic-regexp" option for completeness, so that
the "last one wins" principle can be used to defeat an earlier -E
option, e.g. "git log -E --basic-regexp --grep='<bre>'".  Note that
it cannot have the short "-G" option as the option is to grep in the
patch text in the context of "log" family.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/rev-list-options.txt

@@ -79,6 +79,11 @@ if it is part of the log message.
 
 	Match the regexp limiting patterns without regard to letters case.
 
+--basic-regexp::
+
+	Consider the limiting patterns to be basic regular expressions;
+	this is the default.
+
 -E::
 --extended-regexp::
 
@@ -91,6 +96,11 @@ if it is part of the log message.
 	Consider the limiting patterns to be fixed strings (don't interpret
 	pattern as a regular expression).
 
+--perl-regexp::
+
+	Consider the limiting patterns to be Perl-compatible regexp.
+	Requires libpcre to be compiled in.
+
 --remove-empty::
 
 	Stop when a given path disappears from the tree.

revision.c

@@ -1603,13 +1603,17 @@ static int handle_revision_opt(struct rev_info *revs, int argc, const char **arg
 		return argcount;
 	} else if (!strcmp(arg, "--grep-debug")) {
 		revs->grep_filter.debug = 1;
+	} else if (!strcmp(arg, "--basic-regexp")) {
+		grep_set_pattern_type_option(GREP_PATTERN_TYPE_BRE, &revs->grep_filter);
 	} else if (!strcmp(arg, "--extended-regexp") || !strcmp(arg, "-E")) {
 		grep_set_pattern_type_option(GREP_PATTERN_TYPE_ERE, &revs->grep_filter);
 	} else if (!strcmp(arg, "--regexp-ignore-case") || !strcmp(arg, "-i")) {
 		revs->grep_filter.regflags |= REG_ICASE;
 		DIFF_OPT_SET(&revs->diffopt, PICKAXE_IGNORE_CASE);
 	} else if (!strcmp(arg, "--fixed-strings") || !strcmp(arg, "-F")) {
 		grep_set_pattern_type_option(GREP_PATTERN_TYPE_FIXED, &revs->grep_filter);
+	} else if (!strcmp(arg, "--perl-regexp")) {
+		grep_set_pattern_type_option(GREP_PATTERN_TYPE_PCRE, &revs->grep_filter);
 	} else if (!strcmp(arg, "--all-match")) {
 		revs->grep_filter.all_match = 1;
 	} else if ((argcount = parse_long_opt("encoding", argv, &optarg))) {