interpret_ptr_ reports incorrect ring number, omits bitoff field

[Gary Dixon]

The interpret_ptr_.pl1 subroutine returns a structure giving various information about an input pointer. However, it has several flaws.

1. struc.ring returns a value 1-less than the ring number actually in the input pointer value.
2. struc.bitoff should return (<bit-offset>) if a nonzero bit offset appears in the input pointer value. However, right now, the code does not initialize or place a correct value in that return field.