only random 2x2 matrix is the identity

[mahrud]

This is kinda hilarious:

i223 : tally apply(100, i -> random(QQ^2, QQ^2, MaximalRank => true))

o223 = Tally{| 1 0 | => 100}
             | 0 1 |

[mahrud]

Tangentially, should dim(Module) do something else over a field?

i43 : dim QQ^3

o43 = 0

[mahrud]

Related: #2089 #1229 #999.