log --grep: use the same helper to set -E/-F options as "git grep"

The command line option parser for "git log -F -E --grep='<ere>'"
did not flip the "fixed" bit, violating the general "last option
wins" principle among conflicting options.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

revision.c

@@ -1604,12 +1604,12 @@ static int handle_revision_opt(struct rev_info *revs, int argc, const char **arg
 	} else if (!strcmp(arg, "--grep-debug")) {
 		revs->grep_filter.debug = 1;
 	} else if (!strcmp(arg, "--extended-regexp") || !strcmp(arg, "-E")) {
-		revs->grep_filter.regflags |= REG_EXTENDED;
+		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")) {
-		revs->grep_filter.fixed = 1;
+		grep_set_pattern_type_option(GREP_PATTERN_TYPE_FIXED, &revs->grep_filter);
 	} else if (!strcmp(arg, "--all-match")) {
 		revs->grep_filter.all_match = 1;
 	} else if ((argcount = parse_long_opt("encoding", argv, &optarg))) {

t/t4202-log.sh

@@ -230,6 +230,12 @@ test_expect_success 'log --grep -i' '
 	test_cmp expect actual
 '
 
+test_expect_success 'log -F -E --grep=<ere> uses ere' '
+	echo second >expect &&
+	git log -1 --pretty="tformat:%s" -F -E --grep=s.c.nd >actual &&
+	test_cmp expect actual
+'
+
 cat > expect <<EOF
 * Second
 * sixth