[tex-live] TL Build script install location

[Karl Berry]

I just checked in a change to the source.development/Build script such
that everything gets installed in a subdir inst/, instead of in a bunch
of subdirs directly in Build (bin, include, man, texmf, etc.).  If this
is troublesome to anyone, or some process or another depended on it, let
me know and I can make it optional.  I just was tired of seeing all
those random directories appear.

Also, we can now set the envvar TL_EXTRA_CONF to pass extra flags to
configure, like turning off optimization with CFLAGS=-g, I hope.

k