r3140, r3144, r3298, r3299, r3300, r3307, r3308 merge:

r3140, r3144, r3298, r3299, r3300, r3307, r3308 merge:

resolver fixes:

*) fix memory leak in resolver
*) fix resolver cache rbtree comparison
*) fix segfault in resolver:
   ngx_resolve_name_done() and ngx_resolve_addr_done() did not delete
   contexts from a resolver node waiting list.
*) fix "PTR ." case in address resolver
*) add quotes in an error message,
*) fix resolving an empty name (".")
*) use ngx_resolver_alloc() instead of ngx_resolver_calloc()
   since all fields are filled