Add trim_end() and use it to remove trailing slashes from repo paths

The new function removes all trailing instances of an arbitrary character
from a copy of the supplied char array. This is then used to remove any
trailing slashes from cgit_query_path.

Signed-off-by: Lars Hjemli <hjemli@gmail.com>
diff --git a/parsing.c b/parsing.c
index 74a2484..2c05c09 100644
--- a/parsing.c
+++ b/parsing.c
@@ -168,7 +168,7 @@
 		if (p) {
 			p[0] = '\0';
 			if (p[1])
-				cgit_query_path = xstrdup(p + 1);
+				cgit_query_path = trim_end(p + 1, '/');
 		}
 		cgit_cmd = cgit_get_cmd_index(cmd + 1);
 		cgit_query_page = xstrdup(cmd + 1);