Check for failure to convert boundary_id_type

[roystgnr]

Reason

For efficiency we still default boundary_id_type to 16-bit (signed, for some reason...), so users can easily manually specify a BoundaryName which is an integer (so we try to convert it to an id directly rather than treating it as a string name) but which fails to fit in boundary_id_type (so conversion via istream just gives us 2^15-1) ... and when this happens we don't test for failure afterward.

Design

Check the failbit on that istream, scream an informative error message and die if it's set.

Impact

It's possible for a user's input file to be fine with the current behavior, which would produce e.g. a boundary name of "40000" attached to a boundary id of 32767, which doesn't inherently break anything. But I suspect any users who have so narrowly avoided being bitten by this bug will be fine changing their files to accommodate its fix.