require test point ID or hyphen-minus when description exists

[rhansen]

This avoids parsing ambiguity:

1..1
ok 1 is less than 2

Is "1" part of the description, or is it the test point ID? This change makes it clear that the "1" is the test point ID, and the description is "is less than 2". To force the "1" to be part of the description, that line should read:

ok - 1 is less than 2

or:

ok 1 1 is less than 2

or (preferred):

ok 1 - 1 is less than 2

[Leont]

Yeah, it makes sense for future versions of TAP to require this.