Polish up the malloc allocator to make it more useful for test and

Polish up the malloc allocator to make it more useful for test and
debugging:

Implement an upper limit for allocated memory, specify as:
	-smalloc,40M

Give the malloc allocator its own stats counters so we can see deeply
into what it does.

git-svn-id: svn+ssh://projects.linpro.no/svn/varnish/trunk@2629 d4fa192b-c00b-0410-8231-f00ffab90ce4