#571 VeLa filter parse errors

[David Benn]

Compare the results of parsing the following VeLa filters:

(band = "Johnson B" or band = "Johnson V") and
(obscode = "BDJB" or time >= 2457437.2) and
uncertainty < 0.05

=> OK

(band = "Johnson B" or band = "Johnson V") and
(obscode = "BDJB" or time => 2457437.2) and
uncertainty < 0.05

=> We should report parse error (=>) to user; right now this goes to the console!

(band = "Johnson B" or band = "Johnson V") and
(obscode = "BDJB" or time >= "2457437.2") and
uncertainty < "0.05"

=> Should we allow silent type coercion? Indeed, what is being done when time >= "2457437.2" or uncertainty < "0.05" are hit?

[David Benn]

Both problems remain to be addressed as of 2.20.0

For the first expression, stdout/stderr should be captured just as we now do in the VeLa dialog.

Create a unit test for the second expression.