Don't save "warning: " prefix in lastwarn() message. * error.cc (vwarning): Save base_msg (without "warning: ") to Vlast_warning_message. * error.cc (error_1): Use std::string operators rather than strsave to strip "\n" from fmt string. Simpler syntax avoids having to delete [] memory created with new. * error.cc (warning_1): Strip trailing newline from fmt string as error_1 does. * fail.m: Fix input validation which allowed nonsensical second input with 3 args. Don't post-process warning or error messages from lastwarn or lasterr. Add BIST test for input validation.

Things to do before making a release:

  * Update the version number and release date in configure.ac.

  * Update version number and release year in CITATION.

  * Update the NEWS file.

  * Update the NEWS-<VERSION>.html, index.in, news.in, and download.in
    files for the web site.

  * Copy tarballs to ftp.gnu.org.

  * Post a release announcement to the help@octave.org and
    info-gnu@gnu.org lists.