fixed error in ptrace where scipy csc->csr would fail for large matrices (fixed csr_to_col function to not use transpose)
fixed error in ptrace where scipy csc->csr would fail for large matrices (fixed csr_to_col function to not use transpose)

cgranade/qutip,qutip/qutip,anubhavvardhan/qutip,zasdfgbnm/qutip,cgranade/qutip,zasdfgbnm/qutip,qutip/qutip,anubhavvardhan/qutip