parser: Multiple unary expressions not handled correctly

[Robin]

Contents of a.c:

int main(void) {
    return 13 - - - 10;
}

u@x1 ~/D/g/s/g/m/uc> uparse a.c
Parsing "a.c"
2016/04/11 20:41:19 main.parseFile (uparse.go:69): error: Error in S61: -(26,-), Pos(offset=32, line=3, column=25), expected one of: ident ( int_lit