Change connection.pri[] to int, reverting part of 7215c964e4.

Revert part of commit 7215c964e40afe953787d7831b04182fbaba4662,
"Use real types (enum connection_{state,priority})." of 2005-06-14.

connection.pri[] is indexed by enum connection_priority, but its
elements are merely reference counts; they are never assigned from
or compared to enum connection_priority.  Defining the elements
as int will result in more readable output from GDB.

Noted in bug 920.

src/network/connection.h

@@ -67,7 +67,7 @@ struct connection {
 	 * the struct download it got to the connection, _and_ updates its @pri
 	 * array by the priority it has thus, sum of values in all fields of
 	 * @pri is also kinda refcount of the connection. */
-	enum connection_priority pri[PRIORITIES];
+	int pri[PRIORITIES];
 
 	/* Private protocol specific info. If non-NULL it is free()d when
 	 * stopping the connection. */