more debugging enabled in rawhide kernels.

[Dave Jones]

In tomorrows rawhide kernel, I've enabled a debugging option
called kmemleak. As the name suggests, this tracks memory allocations,
and prints backtraces in cases where the memory is believed to be lost.

Things of note:

- This tracking doesn't come for free, so things may slow down.
  In some cases, perhaps considerably.
- You may see backtraces in dmesg like ..

kmemleak: unreferenced object 0xdb804c40 (size 20):
kmemleak:   comm "swapper", pid 0, jiffies 4294667296
kmemleak:   backtrace:
kmemleak:     [<c04fd8b3>] kmemleak_alloc+0x193/0x2b8
kmemleak:     [<c04f5e73>] kmem_cache_alloc+0x11e/0x174
kmemleak:     [<c0aae5a7>] debug_objects_mem_init+0x63/0x1d9
kmemleak:     [<c0a86a62>] start_kernel+0x2da/0x38d
kmemleak:     [<c0a86090>] i386_start_kernel+0x7f/0x98
kmemleak:     [<ffffffff>] 0xffffffff

  Hold off on reporting them just yet. There are some known traces
  (like that one for eg) which we are aware of already, without needing
  tracking bugs for them.  Hopefully we can nail the obvious bugs &
  false positives quickly.

	Dave