First try at changes file for linalg branch.  Fix test.  Remove debugging.
changes to tests
interface functions for rref added.  Only QQFlint in place so far.
remove unused ring files: QQ, RR, RRR, CC, CCC, coeffirngs-zz, *experim
e/unit-tests now compiles without any warnings on gcc 4.8.0

at least on macosx.
registering mutable matrices now, to destruct when done.  DO NOT USE:

needed as flint caches fmpz's.  BUT: this version crashes.  I am
just checking it in, to test it under different systems.