Add an echo to say we're "Booting..." when the overloaded "boot" Ficl word is

Add an echo to say we're "Booting..." when the overloaded "boot" Ficl word is
executed to better differentiate between loader-specific errors and kernel-
specific errors (if ever any of either).

This type of functionality hasn't been required before the introduction of the
advanced menu system (r222417). Adding this functionality will help different-
iate errors at the loader-level such as a BTX halt caused by heap exhaustion
and errors that may be involved with executing the kernel (wrong architecture
for example). A user can learn that messages before "Booting..." are related to
the loader(8) environment and it's Forth-ilk, while those after are not
related to loader(8) -- the point that loader(8) has ``left the building''.

This patch also includes a man-page update to color.4th(8) as the color logic
moves to a lower-level (from being included by beastie.4th to being included
by loader.4th).

After noticing a delay between execution of the overloaded "boot" FICL word and
the display of text on-screen, gcooper confirmed that the introduction of a
builtin memory test (disabled by adding hw.memtest.tests="0" to loader.conf(5))
was the cause of the delay.

This patch adds an echo to produce "Booting..." when the overloaded "boot" word
is executed (this includes from the interactive command-prompt on all arches,
from the menu system on arches that run the beastie menu, and even those arches
that run the menu but disable it by setting beastie_disable="YES" in
loader.conf(5)). When loader_color="YES" in loader.conf(5), the same message is
produced but in white text on a blue background (only the letters produced have
this background -- opposed to perhaps the entire line).