replace all isFALSE and isTRUE by == FALSE and == TRUE statements

[vincentvanhees]

isFALSE() and isTRUE() are relatively new R functions, by which implementing them in GGIR makes that GGIR does not work on older versions of R. So, I think it is best to stick to using == FALSE and == TRUE to avoid making GGIR too much dependent on the newer R version. Also, there does not seem to be an added value of using those newer function.