irritating GAP warning/error handling

[ThomasBreuer]

I stumbled over the following when dealing with #1057.

julia> f = GAP.evalstr("function() res:= 1; return res; end")
GAP: function(  ) ... end

julia> f()
1

julia> g"\\"
ERROR: Error thrown by GAP: Syntax warning: Unbound global variable in stream:1
function() res:= 1; return res; end;
           ^^^
Syntax warning: Unbound global variable in stream:1
function() res:= 1; return res; end;
                           ^^^
Syntax error: String must end with " before end of file in stream:1
[...]

The GAP syntax warning is not shown in the construction of the function but it is kept in some buffer.
For the later GAP error, the error message gets printed, but first the text of the old syntax warning appears.