Disallow overwriting of dihedral type 9
It is no longer allowed to repeat blocks of parameter of multiple
lines for dihedrals of type 9. It is also no longer allowed to
override parameters or dihedrals of type 9. Both are too complex
to properly check. It is still allowed to repeat parameters blocks
consisting of a single line.
Repeating a block with the same parameters would lead to incorrect
dihedral potentials and forces.
Fixed bug in arrayref.h interfaces.
Fixes #2077.
Change-Id: I802c6714a9700744df4e6b5ea96e41aa82793388