Fix Bugs
http://trac.sagemath.org/sage_trac/ticket/12689 -- (done) Segfault in solve_left for sparse matrices over ZZ
http://trac.sagemath.org/sage_trac/ticket/11358 -- (open!) matrix multiplication over ZZ sometimes gives incorrect results
http://trac.sagemath.org/sage_trac/ticket/12689 -- (done) Segfault in solve_left for sparse matrices over ZZ
http://trac.sagemath.org/sage_trac/ticket/11358 -- (open!) matrix multiplication over ZZ sometimes gives incorrect results