Parser: channel name expressions does not parse a b.1.2 and b.1.2.3 correctly in channel comprehensions

[lausdahl]

The parser does something strange when parsing the following:

aux2 = {c.x.x | x: nat @ x = 3}

this parses as c.x, note the mising x.

A similar issue happens with c.1.2 which gives a number c.(1,2)

[joey-coleman]

This example seems to work fine; we can't reproduce it even on Kenneth's machine.

The second example is related to #215.