Big overhaul of the allocator. Much of the structure is the same, but

Big overhaul of the allocator.  Much of the structure is the same, but
lots of the details changed.  Made the following generalisations:

- Recast everything to be entirely terms of bytes, instead of a mixture
  of (32-bit) words and bytes.  This is a bit easier to understand, and
  made the following generalisations possible...

- Almost 64-bit clean;  no longer assuming 32-bit words/pointers.  Only
  (I think) non-64-bit clean part is that VG_(malloc)() et al take an
  Int as the size arg, and size_t is 64-bits on 64-bit machines.

- Made the alignment of blocks returned by malloc() et al completely
  controlled by a single value, VG_MIN_MALLOC_SZB.  (Previously there
  were various magic numbers and assumptions about block alignment
  scattered throughout.) I tested this, all the regression tests pass
  with VG_MIN_MALLOC_SZB of 4, 8, 16, 32, 64.  One thing required for
  this was to make redzones elastic;  the asked-for redzone size is now
  the minimum size;  it will use bigger ones if necessary to get the
  required alignment.

Some other specific changes:

- Made use of types a bit more;  ie. actually using the type 'Block',
  rather than just having everything as arrays of words, so that should
  be a bit safer.

- Removed the a->rz_check field, which was redundant wrt. a->clientmem.

- Fixed up the decision about which list to use so the 4 lists which
  weren't ever being used now are -- the problem was that this hasn't
  been properly updated when alignment changed from 4 to 8 bytes.

- Added a regression test for memalign() and posix_memalign().
  memalign() was aborting if passed a bad alignment argument.

- Added some high-level comments in various places, explaining how the
  damn thing works.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@2579