memory leak detection patch

[Mike McCormack]

Hi,

This patch is written for MSI, but could be adapted to other code.  It 
keeps a linked list of allocated memory and removes free'd memory from 
the list.

It requires that you change all the HeapAlloc's or mallocs in a dll to 
msi_alloc (for example), but can detect unfree'd memory and invalid free's.

I have discovered quite a few problems in my own code with this patch, 
so hopefully somebody else will find it useful too.

Mike