Restore similar/zero method for MatRingElem with row *and* column arg

These don't really make much sense and I suggest we deprecate them in
the future but for now I want to keep it simple.

src/MatRing.jl

@@ -95,6 +95,14 @@ end
 
 similar(x::MatRingElem, n::Int) = similar(x, base_ring(x), n)
 
+# TODO: deprecate these:
+function similar(x::MatRingElem{T}, R::NCRing, m::Int, n::Int) where T <: NCRingElement
+   m != n && error("Dimensions don't match in similar")
+   return similar(x, R, n)
+end
+
+similar(x::MatRingElem, m::Int, n::Int) = similar(x, base_ring(x), m, n)
+
 @doc raw"""
     zero(x::MatRingElem, R::NCRing, n::Int)
     zero(x::MatRingElem, R::NCRing)
@@ -107,6 +115,10 @@ with defaults based upon the given source matrix ring element `x`.
 zero(x::MatRingElem, R::NCRing=base_ring(x), n::Int=degree(x)) = zero!(similar(x, R, n))
 zero(x::MatRingElem, n::Int) = zero!(similar(x, n))
 
+# TODO: deprecate these
+zero(x::MatRingElem, R::NCRing, r::Int, c::Int) = zero!(similar(x, R, r, c))
+zero(x::MatRingElem, r::Int, c::Int) = zero!(similar(x, r, c))
+
 ################################################################################
 #
 #  Copy and deepcopy