Improve tests:
    + bugs
	+ Trailing ocMissing problems:
	    + allow ocMissing ocSep ocMissing ocClose etc.
	      at end of fn. [ without an error (!) ]
	    + for nParamCount
		+ elide trailing optional params (?)
		  [ or not ? ]
		+ what about functions with trailing optionals ?
		    + behave differently if vararg ? lbound/ubound ?
	    + trailing ocMissing
		+ elide trailers on XML export

    + tests
	+ add missing argument to end of (normal) optional arg
	  function, that doesn't assume '0' default [?]
	    + [ or - better, elide extra ';'s only down to min(nargs) ]
	+ export / add missing ops into formulae where XL does
	  not allow them to be entered / re-import to XL & test.
	+ round-trip to XL ...

    + Do we get an 'svMissing' / 'ocMissing' between
      'ocSep' from the parser ? [ if empty ? (or just ocSpace ?) ]

#if 0
        {   // #84460# May occur if imported from Xcl.
            // The real value for missing parameters depends on the function
            // where it is used, interpreter would have to handle this.
            // If it does remove this error case here, that could also be the
            // time to generate ocMissing in between subsequent ocSep.
            // Xcl import should map missings to values if possible.
            SetError( errParameterExpected );
        }
#endif

+ interpr1.cxx 'GetDBParams' - missing ?
	+ explicit svMissing handling (!?) ...

+ interpr4.cxx:
	+ ScInterpreter::PopDouble() - seems to handle svMissing
	+ also PopString

(gdb) bt
#0  ScCompiler::SetError (this=0xbff77644, nError=508) at /data/OpenOffice/ood680-m4/sc/source/core/tool/compiler.cxx:1088
#1  0xa1cbfa83 in ScCompiler::Factor (this=0xbff77644) at /data/OpenOffice/ood680-m4/sc/source/core/tool/compiler.cxx:3052
#2  0xa1cc000f in ScCompiler::UnionCutLine (this=0xbff77644) at /data/OpenOffice/ood680-m4/sc/source/core/tool/compiler.cxx:3166
#3  0xa1cc016b in ScCompiler::UnaryLine (this=0xbff77644) at /data/OpenOffice/ood680-m4/sc/source/core/tool/compiler.cxx:3190
#4  0xa1cc017f in ScCompiler::PostOpLine (this=0xbff77644) at /data/OpenOffice/ood680-m4/sc/source/core/tool/compiler.cxx:3197
#5  0xa1cc01dd in ScCompiler::PowLine (this=0xbff77644) at /data/OpenOffice/ood680-m4/sc/source/core/tool/compiler.cxx:3209
#6  0xa1cc0263 in ScCompiler::MulDivLine (this=0xbff77644) at /data/OpenOffice/ood680-m4/sc/source/core/tool/compiler.cxx:3223
#7  0xa1cc031b in ScCompiler::AddSubLine (this=0xbff77644) at /data/OpenOffice/ood680-m4/sc/source/core/tool/compiler.cxx:3237
#8  0xa1cc03d3 in ScCompiler::ConcatLine (this=0xbff77644) at /data/OpenOffice/ood680-m4/sc/source/core/tool/compiler.cxx:3251
#9  0xa1cc0459 in ScCompiler::CompareLine (this=0xbff77644) at /data/OpenOffice/ood680-m4/sc/source/core/tool/compiler.cxx:3265
#10 0xa1cc0511 in ScCompiler::NotLine (this=0xbff77644) at /data/OpenOffice/ood680-m4/sc/source/core/tool/compiler.cxx:3279
#11 0xa1cc05dd in ScCompiler::Expression (this=0xbff77644) at /data/OpenOffice/ood680-m4/sc/source/core/tool/compiler.cxx:3300
#12 0xa1cc0837 in ScCompiler::CompileTokenArray (this=0xbff77644) at /data/OpenOffice/ood680-m4/sc/source/core/tool/compiler.cxx:2782

re-factor eOp >= ... inline-functions 'isFunction(eOp)' [ or whatever ]


Factor::3052:

    + detects fn start
    + iterates over args
	+ NextToken()
	    - odd semantic
	+ Expression
	    - PutCode's a full expression ?
		+ via NotLine (?) ... [ cf. above ]
	    + -> UnaryLine

* Where to hack the compiler

    CompileString:

    + ScCompiler::IsOpCode - catches ';' & generates ocSep
	+ need to spew a double op-code from it (?)
	+ where is this inserted ?

		if( eLastOp == ocSep &&
			pRawToken->GetOpCode() == ocSep )
		{
			fprintf( stderr, "Add ocMissing before sep\n");
			// FIXME: should we check for known functions with
			// optional args so the correction dialog can do better ?
			ScRawToken aMissingToken;
			aMissingToken.SetOpCode( ocMissing );
			if ( !pArr->AddToken( aMissingToken ) )
			{
				fprintf (stderr, "Error adding ocMissing\n");
				SetError(errCodeOverflow); break;
			}
		}

excform.cxx:
	// #84453# skip missing parameters at end of parameter list
	while( (nSkipEnd < nLast) && aPool.IsSingleOp( eParam[ nSkipEnd + 1 ], ocMissing ) )

xeformula.cxx:
        /*  #i37355# insert tMissArg token for missing parameters --
            Excel import filter adds ocMissing token (handled in Factor()),
            but Calc itself does not do this if a new formula is entered. */
        switch( aTokData.GetOpCode() )
        {