Matrix.det_bareis is sensitive to ImmutableMatrix
sympify args of MatrixExpr functions

Otherwise Matrix objects can creep in
explicitly merge MatrixBases in MatAdds
matmul merge_explicit rule
matadd/matmul: fix doc and unittests

Signed-off-by: Thomas Hisch <thomas.hisch@ims.co.at>
Merge pull request #17 from thisch/mrocklin-matexpr-sympify

matadd/matmull fix unit and doctests
MatMul merge explicit does not commut matrices
Merge pull request #7250 from mrocklin/matexpr-sympify

Matexpr sympify
Fix #7206: Equality with matrices.

Equality was changed to support objects with an _eval_Eq method.  This allows
objects to define alternative algorithms for determining equality.  Such a
method was implemented in ImmutableMatrix.