8FUNCTIONS: iaunit - CYANA function

Synopsis: iaunit(<integer>) = <integer>

This function returns the index of the rigid unit to which the atom
with the given atom index belongs, i.e. the index of the dihedral
angle immediately preceding the selected atom.

Optionally, the <integer> atom index can be replaced by a string
consisting of the atom name and the residue number, separated by a
blank or a period, '.'.
