Problem was that the malloc-replacing tools (memcheck, addrcheck, massif,
helgrind) would assert if a too-big malloc was attempted. Now they return 0 to
the client. I also cleaned up the code handling heap-block-metadata in Massif
and Addrcheck/Memcheck a little.
This exposed a nasty bug in VG_(client_alloc)() which wasn't checking if
find_map_space() was succeeding before attempting an mmap(). Before I added
the check, very big mallocs (eg 2GB) for Addrcheck were overwriting the client
space at address 0 and causing crashes.
Added a regtest to all the affected skins for this.
git-svn-id: svn://svn.valgrind.org/valgrind/trunk@2462
