Flagging ambiguity in interlingua checking

I've just checked in code to catch cases where interlingua is
ambiguous, in the sense of generating multiple different surface
strings in the interlingua grammar. This is most likely to occur in
AFF, when the to-interlingua rules are underconstrained and the
interlingua is only partially instantiated. The following Japanese
-> Interlingua example in MedSLT illustrates:

>> doko ga itami masu ka

Source: doko ga itami masu ka
Target: WH-QUESTION pain be where PRESENT ACTIVE
Other info:
n_parses = 1
parse_time = 0.297
source_representation = [null=[path_proc,itamu], null=[tense,present],
                      null=[utterance_type,question], subject=[body_part,doko]]
source_discourse = [null=[utterance_type,question], subject=[body_part,doko],
                 null=[tense,present], null=[path_proc,itamu]]
resolved_source_discourse = [null=[utterance_type,question], subject=[body_part,doko],
                          null=[tense,present], null=[path_proc,itamu]]
resolution_processing = trivial
interlingua = [loc=[loc,where], arg1=[secondary_symptom,pain], null=[tense,present],
            null=[utterance_type,whq], null=[verb,be], null=[voice,active]]
interlingua_surface = WH-QUESTION pain be where PRESENT ACTIVE
other_interlingua_surface = [WH-QUESTION pain be above-loc where PRESENT ACTIVE,
                          WH-QUESTION pain be around-loc where PRESENT ACTIVE,
                          WH-QUESTION pain be between-loc where PRESENT ACTIVE,
                          WH-QUESTION pain be in-loc where PRESENT ACTIVE,
                          WH-QUESTION pain be under-loc where PRESENT ACTIVE]