Improve error message for mixing equation/algorithm syntax (from MathCore)

[Peter Aronsson]

The model test below returns the message:
{{{--- [12] 11:19:09 Syntax error(s) in model test ---
test(8) : error: expecting an identifier, found 'if'}}}
{{{model test

Real y;

equation

if true then

y:=1;

else

y:=2;

end if;

end test;}}}

The error is that ':=' is used instead of '='. It is very easy to mix these things up for a novice user so a better error message is needed.

[Peter Aronsson]

(MathCore TRAC ​http://intranet/trac/mathmodelica/ticket/1693)

[Martin Sjölund]

The new parser outputs:
[a.mo:5:6-5:7:writable] Error: No viable alternative near token: :=

Is this good enough or should we have a customized error message?

[Peter Aronsson]

This is the most common syntactic error that new users do, so I think that a customized error message could be good for just this case.

[Martin Sjölund]

This now yields
[a.mo:5:6-5:7:writable] Error: Parse error: Equations can not contain assignments (':='), use equality ('=') instead (in my local copy)

(Previously, only the reverse, equation syntax in algorithms, was handled as a special case.)

[Martin Sjölund]

Fixed in r7521