Add '--fixed-strings' option to "git log --grep" and friends

Add support for -F | --fixed-strings option to "git log --grep"
and friends: "git log --author", "git log --committer=<pattern>".
Code is based on implementation of this option in "git grep".
Signed-off-by: NJakub Narebski <jnareb@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/git-rev-list.txt

@@ -31,6 +31,7 @@ SYNOPSIS
 	     [ \--(author|committer|grep)=<pattern> ]
 	     [ \--regexp-ignore-case | \-i ]
 	     [ \--extended-regexp | \-E ]
+	     [ \--fixed-strings | \-F ]
 	     [ \--date={local|relative|default|iso|rfc|short} ]
 	     [ [\--objects | \--objects-edge] [ \--unpacked ] ]
 	     [ \--pretty | \--header ]

Documentation/rev-list-options.txt

@@ -153,6 +153,11 @@ limiting may be applied.
 	Consider the limiting patterns to be extended regular expressions
 	instead of the default basic regular expressions.
 
+-F, --fixed-strings::
+
+	Consider the limiting patterns to be fixed strings (don't interpret
+	pattern as a regular expression).
+
 --remove-empty::
 
 	Stop when a given path disappears from the tree.

revision.c

@@ -942,6 +942,7 @@ int setup_revisions(int argc, const char **argv, struct rev_info *revs, const ch
 	int left = 1;
 	int all_match = 0;
 	int regflags = 0;
+	int fixed = 0;
 
 	/* First, search for "--" */
 	seen_dashdash = 0;
@@ -1238,6 +1239,11 @@ int setup_revisions(int argc, const char **argv, struct rev_info *revs, const ch
 				regflags |= REG_ICASE;
 				continue;
 			}
+			if (!strcmp(arg, "--fixed-strings") ||
+			    !strcmp(arg, "-F")) {
+				fixed = 1;
+				continue;
+			}
 			if (!strcmp(arg, "--all-match")) {
 				all_match = 1;
 				continue;
@@ -1293,8 +1299,10 @@ int setup_revisions(int argc, const char **argv, struct rev_info *revs, const ch
 		}
 	}
 
-	if (revs->grep_filter)
+	if (revs->grep_filter) {
 		revs->grep_filter->regflags |= regflags;
+		revs->grep_filter->fixed = fixed;
+	}
 
 	if (show_merge)
 		prepare_show_merge(revs);