ellpack matrix now deallocates degrees array; failure to do so was causing a memory leak
Fixed some of the reference counting in matrices. Basic matrix tests run without memory leaks.
Added call to destructor in default kernel for setting a matrix entry with reallocation. Corresponding matrix test no longer leaks memory
Minor change to LDU sparsity pattern routine eliminates a memory leak
Implemented reference counting for linear operators. Operator algebra test has no memory leaks now.