2015 Code Sprint: Eliminate useless return statements after error (). * data.cc, graphics.cc, graphics.in.h, ls-mat4.cc, ls-mat5.cc, oct-fstrm.cc, oct-stream.cc, oct-strstrm.cc, __delaunayn__.cc, ov-base-int.cc, ov-classdef.h, ov-complex.cc, ov-cx-sparse.cc, ov-fcn-inline.cc, ov-float.cc, ov-flt-complex.cc, ov-java.cc, ov-range.cc, ov-re-sparse.cc, ov-scalar.cc, ov-struct.cc, ov-usr-fcn.cc, ov.cc, op-cm-cm.cc, op-cm-m.cc, op-cm-scm.cc, op-cm-sm.cc, op-fcm-fcm.cc, op-fcm-fm.cc, op-fm-fcm.cc, op-fm-fm.cc, op-m-cm.cc, op-m-m.cc, op-m-scm.cc, op-m-sm.cc, op-scm-cm.cc, op-scm-m.cc, op-scm-scm.cc, op-scm-sm.cc, op-sm-cm.cc, op-sm-m.cc, op-sm-scm.cc, op-sm-sm.cc, pt-exp.cc: Eliminate useless return statements after error ().

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.