realtime.in:  sleep after loading shmdrv to allow it to initialize

fixes this message:

shmdrv_driver_fd: cant access /dev/shmdrv - permission denied; shmdrv.rules not installed?
Makefile:  move directory creation into install-dirs target

...and install-kernel-dep depends on install-dirs
realtime and rtapi.conf scripts:  fix non-RIP paths

- pick up ${prefix}
- explicit paths to linuxcnc binaries
rtapi.conf:  set kernel module path for non-RIP installs