strange error messages with (ill-formed) meta-terms (#0892)

[eclipse 1]: var(V{suspend:s}).

V = V
yes.

works, but

(first example is adapted from the example in the Bips pages for
nonground/2)

[eclipse 1]: nonground(V{s}).
undefined variable attribute in trans_meta_in(V, _151, eclipse)
illegal stream specification in stream_info_(abort, 13, _198)

[eclipse 1]: var(V{s}).
undefined variable attribute in trans_meta_in(V, _151, eclipse)
illegal stream specification in stream_info_(abort, 13, _198)

-- second error message did not appear in 4.2.
-- first error message is also not very helpful