Adding autogen.sh and removing autogenerated files.

Those should be generated and distributed as part of the release process.
Build fix for MacOS X.
Disabling default compilation of xshogi.
Fix buffer overflow, patch by Typone Alfredo (alfredo@tupone.it).
Changing license to GPL3 (and bumping version to 1.4.0).
Add missing info headers
Fix a function prototype.
Do not attempt to outguess system headers by (re)defining errno.

Recent glibc define error as a cpp macro expanding to a function
call.  Thus, "extern int errno" should cause a link-time undefined
symbol when errno.h is not included.  Here it is, and gcc complains
with the following cryptic warning:

../../gnushogi/sysdeps.c: In function 'ElapsedTime_FIONREAD':
../../gnushogi/sysdeps.c:97: warning: function declaration isn't a prototype
Fix integer overflow caused by bad use of binary operator.

Guess this may make the AI more accurate :)

Problem caught by gcc:

../../gnushogi/search.c: In function 'search':
../../gnushogi/search.c:887: warning: overflow in implicit constant conversion

A quick audit only revealed a place where another logical AND was
tested using a curious idiom, so let's make it consistent at the same
time.
Don't intercept INT and QUIT signals, and use USR1 instead of QUIT for
communication.

This braindead use of SIGINT causes problem when a frontend is
interrupted with Ctrl-C: if gnushogi is waiting for input, it would
enter a tight loop trying to read stdin, eating 100% CPU.
Statify functions not used outside their compilation unit.
Fixes segfault in gnushogi when asking for help.

Closes Debian Bug#434139.
Deal with warnings raised by -Wformat-security.
Add support for building gnushogi and xshogi out of source tree.