Graphs now include a reference count, and are made immutable if there is more than one reference to each graph.
Fixed bugs in the copy constructors of cs and ellpack graphs
Started making linear operator data type
Making sparse matrices an extension of linear operators compiles and works
Started adding linear operator tests
Adding two linear operators works.
Multiplying linear operators works.
Bug fix. Passes tests with Intel Fortran compiler.
Overloaded assignment of linear operator pointers