- Make pointer easier to control when moving slowly.
- Increase chance of vertical scrolling as vertical scrolling is used more often.

Submitted by:	Huang Wen Hui <huanghwh@gmail.com>
MFC after:	2 weeks
Prevent fdt data loaded from a file from overwriting the kernel environment,
by having uboot_autoload() do the fdt setup (which may load a file) rather
than waiting until we're actually in the process of launching the kernel.

As part of making this happen...
 - Define LOADER_FDT_SUPPORT on the uboot/lib compile command line when
   MK_FDT is set.
 - Make fdt_setup_fdtb() public.
 - Declare public fdt_whatever() functions in a header instead of using
   scattered extern decls in .c files.
Expose a few DTrace parameters as sysctls under kern.dtrace and add
descriptions for several existing sysctls.

PR:		187027
Submitted by:	Fedor Indutny <fedor@indutny.com> (original version)
MFC after:	2 weeks