Error in object type check for Filesystem.Tar.

Imported from http://bugzilla.roxen.com/bugzilla/show_bug.cgi?id=1594

Reported by Martin Stjernholm mast@roxen.com

I do not think that the following program contains an error:

static Filesystem.Tar tar;

int main()
{
  if( catch( tar = Filesystem.Tar("config_interface/docs.tar") ) )
    tar = 0;
}

But 7.2 thinks there's a type problem in the first assignment:

/home/mast/foo.pike:5:Bad type in assignment.
/home/mast/foo.pike:5:Expected: object(implements 65605)
/home/mast/foo.pike:5:Got     : object(is 65611)
/home/mast/foo.pike:5:Missing identifier "_Tar".
Pike: Failed to compile script:
Compilation failed.