Restore previous copyright information that got removed by error.

This reverts part of commit 82b026e6376b640a4d3409a461dd6bd83708e33e,
which changed too much of the copyright headers when changing license
to GPL3.
Clarify configure options that only relate to xshogi
Add .gitignore file
Remove excessive boilerplate duplication from dspwrappers.
Allow configure --without-curses.

Not finding libcurses was surely causing problems, we now also proceed cleanly
in that case.
Honor LDFLAGS at link-time.
Remove text of the GPL (v2) from texinfo doc, it did not format any more though TeX.
Use @ifnotex and not @ifinfo, or HTML does not get its ToC.
Critical texinfo doc formatting fixes.

* "@sp 1" everywhere look ugly today
* ASCII rendering of boards requires @verbatim
Start to fill NEWS, rotate pre-git logs to ChangeLog.old.
Initiate new ChangeLog using git2cl.
Don't cause autogen.sh to run configure.
Remove hack previously used to insert diags into generated HTML.

Useless since db5c540ff7e9dd176f797b50031141e2c2059456.
Rework doc-handing make rules and remove generated files from version control.

Newer texinfo.tex was imported from texinfo 5.1.
Start of a "make dist" target.

The old one uses a script that was never published...
Rename configure --with-xshogi to --enable-xshogi for correctness.
Restore SIGINT for stopping gnushogi when thinking.

SIGINT is unfortunately part of the protocol inherited from gnuchess4,
and is used by xboard as such.  So this was not a proper fix for the
original issue.

This reverts commit 00e10bc4a760150665436b17c50abf264f28d435,
"Don't intercept INT and QUIT signals, and use USR1 instead of QUIT for".
Detect EOF waiting for user input in xshogi and raw modes, and trigger exit.

No idea why the raw implementation of ExitShogi() did not call exit().
Even after detecting EOF, we were thrown into a tight loop...
Regularly check for user input when searching, to have a chance to catch EOF from engine.

When an engine quits without terminating a searching gnushogi, it would
continue to search and never realize there was no reason to continue.

This is a poll-based implementation of what H.G.Muller wrote for WIN32 to
circumvent the lack of UNIX signals there.
Finally get rid of that highly non-standard use of SIGINT.

People will at last be able to Ctrl-C gnushogi :)