linuxrc: use "quiet" cmdline argument for a really quiet initramfs initialization

"quiet" is already used by the kernel to avoid printing messages on the
console unless they are errors or warnings. Genkernel should do the same
wrt its initramfs initialization code.
This has also the advantage of improving the boot speed.
linuxrc: run the debug shell multiple times, add a hook before switch_root
gen_compile: fix iscsi module path install, s/RELEASE/KV
genkernel: add simple udev support, include udev into initramfs if --udev
gen_compile: use LVM from system for the initramfs
gen_compile: use DMRAID from system, don't compile our own
gen_compile: use MDADM from system
linuxrc: don't try to be too smart wrt resolving REAL_ROOT symlink

This breaks LVM support with udev, don't do it, there is absolutely no reason
gen_initramfs: use portage-utils to determine the lvm2 udev rules files
gen_initramfs: differentiate between vital udev rules and non-vital
Merge remote-tracking branch 'origin/master' into udev-love+plymouth

Conflicts:
	defaults/initrd.scripts