noninformative error msg with module declaration mistake

[GoogleCodeExporter]

I wrote
concrete XEng of X = Y ** {...}

instead of 
concrete XEng of X = YEng ** {...}

and I got this hard to interprete error:
cannot unify the information
    lincat A = {s : ResEng.AForm => Str} ;
    lindef A = \str_0 -> {s = table ResEng.AForm {
                                q_A__0 => str_0
                              }} ;
in module CatEng with
    cat A ;
in module Cat

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It was v hard to find this error, it would be good to replace error msg with 
sth more informative

Original issue reported on code.google.com by adam.sla...@gmail.com on 14 Apr 2011 at 9:39