Added safety checks to Array::xelem There's no reason to have a method which never checks invariants, ever. Added debugging checks to Array::xelem to help catch and debug out-of-bounds errors and reference overlap * configure.ac: Added configuration option for uniqueness-checking with xelem * jit-typeinfo.cc (octave_jit_paren_scalar): Call const Array::xelem rather than Array::xelem * Array-util.h, Array-util.cc (check_out_of_range): Extract common pattern to method (check_index): Methods to check index is in-bounds (compute_index): Added bool parameter check. does not check bounds when check is false and BOUNDS_CHECKING is off * Array.h, Array.cc (xelem): Use methods from Array-util.h to compute indices (is_unique): Check if this is the only reference to data * CmplxQR.cc, dbleQR.cc, fCmplxQR.cc, floatQR.cc (form): Move second assignment to after the call to xelem * lo-array-gripes.h, lo-array-gripes.cc (gripe_modifying_nonunique): Added error message for when non-const xelem is called on non-unique array