Values returned by solve methods should match type of rhs

`solve` methods involving a `CholmodFactor` object, whether called
directly or indirectly through methods for `\`, `Ac_div_B`, etc. now
return the same type of object as the right hand side.  If the rhs is
an `Array` they return an `Array`.  Previously these methods returned
a `CholmodDense` or `CholmodSparse` object.