Previously, each Arena has a linked list of Superblocks, which can

Previously, each Arena has a linked list of Superblocks, which can
make VG_(arena_free) expensive if many superblocks have to be checked
before the right one is found.  This change gives the arena a
dynamically expanding sorted array of superblocks, so that finding the
superblock containing an about-to-be-freed block (findSb) is now
O(log2 n) rather than linear in the number of superblocks in the
arena.  Patch from Christoph Bartoschek.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@6771