isdir.m: Make m-file a legacy function (bug #54489) * isdir.m: Note that function is not recommended in docstring. Add 1-time warning about function being obsolete. Add first time BIST test to provoke and suppress warning. * scripts/legacy/module.mk, scripts/miscellaneous/module.mk: Move isdir.m from miscellaneous/ dir to legacy/ dir. * NEWS: Announce change to legacy function. * syscalls.cc (Fstat): Add isfolder to @seealso link. * utils.cc (Fis_absolute_filename, Fis_rooted_relative_filename, Fmake_absolute_filename): Replace isdir with isfolder in @seealso links. * uigetdir.m, uigetfile.m, uiputfile.m, which.m, copyfile.m, mkdir.m, movefile.m, tempdir.m, unpack.m, what.m, __print_parse_opts__.m, compare_plot_demos.m, rundemos.m, runtests.m: Replace instances of isdir with isfolder in core Octave.

--- a/NEWS	Mon Aug 13 11:41:17 2018 -0700
+++ b/NEWS	Mon Aug 13 12:17:58 2018 -0700
@@ -79,6 +79,7 @@
       ---------------------|------------------
       findstr              | strfind
       flipdim              | flip
+      isdir                | isfolder or dir_in_loadpath
       isequalwithequalnans | isequaln
       isstr                | ischar
       setstr               | char