[PATCH 04 of 23] mx_ops: add "probe" callback

[Damien Riegel]

# HG changeset patch
# User Damien Riegel <damien.rie...@gmail.com>
# Date 1462465197 14400
#      Thu May 05 12:19:57 2016 -0400
# Node ID 2a589a2f269240ff4ed7f769f3a5b6053eaf3ef7
# Parent  88576ba91bdf9ee164eeba9c68df8566b4095126
mx_ops: add "probe" callback

Each mailbox will define this callback and return true if it can handle
the path given as parameter.

diff -r 88576ba91bdf -r 2a589a2f2692 mutt.h
--- a/mutt.h    Thu May 05 14:11:34 2016 -0400
+++ b/mutt.h    Thu May 05 12:19:57 2016 -0400
@@ -871,6 +871,7 @@
 struct _context;
 
 struct mx_ops {
+  int (*probe)(const char *path);
   int (*close)(struct _context *);
 
 };