Add new method compileN which generalises compile0 & compile1. Supporting this is a new GVM instruction check_mark. N.B. As part of this investigation I now suspect the GVM instruction END_MARK is faulty (does not bind VMCOUNT) and is not used correctly either.
Added new idiom for iterating over the children of a MinX element. We now support the following elegant construction:

typedef shared< Mnx > SharedMnx;
SharedMnx node = ...
...
for ( MnxChildIterator chit( node ); !!chit; ++chit ) {
    SharedMnx child = *chit;
    …
}
Enhanced common2gnx (and cstyle2gnx) so that they correctly handle the case of binding to a (nested) sequence of variables.
Assigning to multiple variables implemented.
Fixed defect in applying local variables to expressions of known arity.