gauge(...); does not work

Imported from http://bugzilla.roxen.com/bugzilla/show_bug.cgi?id=1793

Reported by Johan Schön js@roxen.com

This program:

int main()
{
  string foo;
  gauge(foo="");
}

gives the following error:

test.pike:4:Bad argument 2 to `-.
test.pike:4:Expected: !function(!(object | mixed) ... : mixed) & function | function(int, int ... : int) | !function(!float ... : mixed) & function(int | float, int | float ... : float) | function(array((0=mixed)), array ... : array(0)) | function(mapping((1=mixed):(2=mixed)), mapping | array | multiset ... : mapping(1:2)) | function(multiset((3=mixed)), multiset : multiset(3)) | function(string, string ... : string)
test.pike:4:Got     : function(int, string, int : void | mixed)
Pike: Failed to compile script:
Compilation failed.