Use tempname() rather than tmpnam() in core Octave. * scripts/miscellaneous/tempname.m: Removed m-file as function is now C++. * scripts/miscellaneous/tmpnam.m: New m-file is an alias that calls tempname. * scripts/miscellaneous/module.mk: Add tmpnam.m to build system. * io.txi: Place tempname, tempdir, P_tmpdir docstrings in section on temporary files. * system.txi: Remove tempname, tempdir, P_tmpdir docstrings from generic system functions section of manual. * dirfns.cc, dlmread.cc, md5sum.cc, ov-fcn-handle.cc: Replace instances of tmpnam with tempname in BIST code. * file-io.cc (Ftempname): Change DEFUNX for tmpnam to DEFUN for tempname. Remove seealso links to tmpnam. * ftp.m, playaudio.m, wavwrite.m, imformats.m, imread.m, imwrite.m, imageIO.m, csvwrite.m, dlmwrite.m, fileread.m, importdata.m, textread.m, textscan.m, genvarname.m, unpack.m, install.m, legend.m, __gnuplot_drawnow__.m, copyobj.m, hgsave.m, print.m, __ghostscript__.m, __gnuplot_get_var__.m, __gnuplot_ginput__.m, __gnuplot_print__.m: Replace tmpnam with tempname in core code. * build-sparse-tests.sh, io.tst, prefer.tst, system.tst: Replace tmpnam with tempname in test code.