Fix author ident cache being keyed by email only

This addresses the issue where an author name change "wins" and tig
shows it for all historical commits by same email under old names

Addresses jonas#526 , jonas/tig/jonas#424

include/tig/util.h

@@ -75,6 +75,7 @@ struct time {
 };
 
 struct ident {
+	const char *key;
 	const char *name;
 	const char *email;
 };

src/parse.c

@@ -267,25 +267,31 @@ get_path(const char *path)
 	return entry->path;
 }
 
-DEFINE_STRING_MAP(author_cache, const struct ident *, email, 32)
+DEFINE_STRING_MAP(author_cache, const struct ident *, key, 32)
 
 /* Small author cache to reduce memory consumption. No entries
  * are ever freed. */
 struct ident *
 get_author(const char *name, const char *email)
 {
-	struct ident *ident = string_map_get(&author_cache, email);
+	char key[SIZEOF_STR + SIZEOF_STR];
+	struct ident *ident;
 
+	string_format(key, "%s%s", email, name);
+
+	ident = string_map_get(&author_cache, key);
 	if (ident)
 		return ident;
 
 	ident = calloc(1, sizeof(*ident));
 	if (!ident)
 		return NULL;
+	ident->key = strdup(key);
 	ident->name = strdup(name);
 	ident->email = strdup(email);
-	if (!ident->name || !ident->email ||
-	    !string_map_put(&author_cache, email, ident)) {
+	if (!ident->key || !ident->name || !ident->email ||
+	    !string_map_put(&author_cache, key, ident)) {
+		free((void *) ident->key);
 		free((void *) ident->name);
 		free((void *) ident->email);
 		free(ident);