doc: miscellaneous documentation improvements * aspell-octave.en.pws: Add new words to spelling dictionary. * expr.txi: Use hyphens in "element-by-element" construction. * install.txi: Miscellaneous docstring improvements. * mk_undocumented_list: Update script. * xlim.m: Add ylim and zlim to function index. * data.cc: Add inf and nan to to function index. * file-io.cc: Add octave_tmp_file_name to function index. Expand docstring for SEEK_CUR and SEEK_END. * help.cc: Miscellaneous docstring improvements. * syscalls.cc: Improve docstrings for F_XXXX series of functions.

--- a/scripts/plot/xlim.m
+++ b/scripts/plot/xlim.m
@@ -17,6 +17,10 @@
 ## <http://www.gnu.org/licenses/>.
 
 ## -*- texinfo -*-
+## @c List other forms of function in documentation index
+## @findex ylim
+## @findex zlim
+##
 ## @deftypefn  {Function File} {@var{xl} =} xlim ()
 ## @deftypefnx {Function File} {} xlim (@var{xl})
 ## @deftypefnx {Function File} {@var{m} =} xlim ('mode')