This commit adds even more correct handling of parameters
with paths if they contain leading or trailing spaces, and
also fixes problems if the user specified an explicit path
to additional directories, but these directories match the
non-standard datadir path - in this In this case, additional
subdirectories must be treated (in relation to datadir) as
if the path was not specified or implicitly specified via
"." or "./", but the script code before this fix worked
as if the user had specified separate paths for each of
the additional subdirectories (although in fact they
point to the same place where datadir points).

This fix does not contain separate tests, as tests will
be part of the main commit(s). This fix has been made as
a separate commit to facilitate review for major substantive
fixes related to MDEV-30157 and MDEV-28669.