Add Triangular.

This doesn't build because Triangular isn't defined yet when
factorization is built.
Reorder methods.

Note: produces ambiguity warning at compile time
Warning: New definition
    A_mul_Bc could not show value of type Tuple at
linalg/factorization.jl:370
is ambiguous with:
    A_mul_Bc could not show value of type Tuple at
linalg/triangular.jl:180.
To fix, define
    A_mul_Bc could not show value of type Tuple
before the new definition.
fix ambiguity warning for A_mul_Bc
Change QRCompactWYQ.T to be Triangular
Unwrap T::Triangular when calling gemqrt!
Add test of QRCompactWY(Q) machinery
Merge pull request #7649 from JuliaLang/cjh/fix-7304

Label QRCompactWY.T as Triangular