FSAL_LUSTRE: deal with different headers across 2.1 and 2.4 (and higher)

Conflicts:

	src/FSAL/FSAL_LUSTRE/export.c
	src/FSAL/FSAL_LUSTRE/fsal_handle.h
	src/FSAL/FSAL_LUSTRE/handle.c
	src/FSAL/FSAL_LUSTRE/xattrs.c