about: allow to give head from query

Reading the README from repository used to be limited to default
branch or a branch given in configuration. Let's allow a branch
from query if not specified explicitly.

Signed-off-by: Christian Hesse <mail@eworm.de>

cgit.c

@@ -507,9 +507,11 @@ static inline void parse_readme(const char *readme, char **filename, char **ref,
 	/* Check if the readme is tracked in the git repo. */
 	colon = strchr(readme, ':');
 	if (colon && strlen(colon) > 1) {
-		/* If it starts with a colon, we want to use
-		 * the default branch */
-		if (colon == readme && repo->defbranch)
+		/* If it starts with a colon, we want to use head given
+		 * from query or the default branch */
+		if (colon == readme && ctx.qry.head)
+			*ref = xstrdup(ctx.qry.head);
+		else if (colon == readme && repo->defbranch)
 			*ref = xstrdup(repo->defbranch);
 		else
 			*ref = xstrndup(readme, colon - readme);

cgitrc.5.txt

@@ -579,11 +579,11 @@ repo.readme::
 	verbatim as the "About" page for this repo. You may also specify a
 	git refspec by head or by hash by prepending the refspec followed by
 	a colon. For example, "master:docs/readme.mkd". If the value begins
-	with a colon, i.e. ":docs/readme.rst", the default branch of the
-	repository will be used. Sharing any file will expose that entire
-	directory tree to the "/about/PATH" endpoints, so be sure that there
-	are no non-public files located in the same directory as the readme
-	file. Default value: <readme>.
+	with a colon, i.e. ":docs/readme.rst", the head giving in query or
+	the default branch of the repository will be used. Sharing any file
+	will expose that entire directory tree to the "/about/PATH" endpoints,
+	so be sure that there are no non-public files located in the same
+	directory as the readme file. Default value: <readme>.
 
 repo.section::
 	Override the current section name for this repository. Default value: