Bypass Operator: Produce a Warning istead of Error when only Connecting with Bypass

[moiri]

The following example should produce a warning instead of an error:

A = box a(out bypass)
B = box b(out x)
C = box c(in x, in bypass)

connect A:B:C

To fix the warning use an abstract net instead of a composed net:

A = box a(out bypass)
B = box b(out x)
C = box c(in x, in bypass)

N = B:C
connect A.N