Merge non-apr-util parts of r1438957 from trunk:

    Add valgrind support
    
    Teach valgrind about apr pools, allocators, and bucket allocators
    if --with-valgrind is passed to configure.
    
    This has less impact on program behavior and performance than compiling
    with complete pool-debugging. Even with valgrind support compiled in,
    the performance impact if not running under valgrind should be minimal.
    
    It may make sense to use pool-debugging together with valgrind support
    because pool-debugging does not help with allocators and bucket
    allocators.

The macros in include/private/apr_support.h (which does not exist in 1.6) were
folded into memory/unix/apr_pools.c. All other users of the macros are in
apr-util in 1.x and could not use a header that is private to apr, anyway.


git-svn-id: https://svn.apache.org/repos/asf/apr/apr/branches/1.6.x@1594699 13f79535-47bb-0310-9956-ffa450edef68