More semicolon tests

[jkeiser]

Specifically, "missing operand" related tests. "1; + 2", "1;+ 2", "1 +; 2" and "1 + ; 2". Also parentheses tests: "(1;)" and " (1 ; )" should return nothing, and "(1;2)" should return 2. Finally, interaction with newline: "1;\n2" should return 2, "1\n;2" and "1\n;\n2" as well. "1;2\n3;4" should return 4.

I haven't figured out a good way to test whether 1;2 and 3;4 are children of the \n, even though that's how it's designed at the moment. If it has no visible effect, I suppose it doesn't mean anything.