- fix building out-of-tree;

- fix building out-of-tree;
  to test, checkout the source (let's assume /scratch/src/busybox), then
  mkdir /tmp/bb ; cd /tmp/bb
  make top_srcdir=/scratch/src/busybox O="$(pwd)" -f /scratch/src/busybox/Makefile allyesconfig check
- default to O=$(pwd) if no O was specified. Now you can just specify
  the top_srcdir (without O=/somewhere) to create the obj-tree in pwd.
- make "make configtarget buildtarget" work. Previously this didn't
  work due to how HAVE_DOT_CONFIG was evaluated. Two separate steps were
  needed before, e.g. make config ; make busybox.
- remove some unneeded variables from Rules.mak (BB_SRC_DIR from Mr.
  ldoolitt@recycle.lbl) which suggest that the stuff fixed above
  didn't work before.
- move selinux libraries to where they belong (from Makefile to Rules.mak)
- update the docs to mention svn instead of cvs and provide an example
  for building out-of-tree in INSTALL.