Finds the FSL version from FSLDIR/etc/fslversion
fsl_version()
fslversion()
fsl_version_gt5()
If the version file does not exist, it will throw a warning, but it will return an empty string. Otherwise it will be a string of the version.
This will use fsldir()
to get the directory
if (have_fsl()) {
fslversion()
fsl_version()
}