[boost] [shared_ptr] Patch adding weak_use_count and weak_from_this

Subject: [boost] [shared_ptr] Patch adding weak_use_count and weak_from_this
From: Brent Lewis (coder0xff_at_[hidden])
Date: 2012-09-12 18:00:35

These are useful for debugging, similarly to shared_ptr::use_count.
Specifically, you can check for dangling pointers by replacing ordinary
pointers with weak pointers, and checking the count inside a destructor.
The patch is for boost 1.49 and is attached.