configure.in:  check for -lrt & add to LDFLAGS for both posix and rt-preempt
rtapi/Submakefile:  fix brain-dead linker args to ulapi.so
hal/hal_lib.c:  remove flavor-specific #ifdef
module_helper/Submakefile:  cleanup
rtapi backend cleanups:  move #includes from .h to .c; other noops

Flavor specific #includes (mostly) don't need to be publicized.

Remove an RTAI conditional (assuming nobody uses RTAI < v3.0)

Remove obsolete REV_CODE and some comments