[Patch] Supported SWIG version(Re: Supported SWIG version on swig-py3)

Hi, I updated the patch to restrict supported SWIG version
posted before, <4ea8a16b-f04b-ab8c-8794-60a244294d6f_at_poem.co.jp>.

In build system:
* Make symbolic link for *.so files in build tree on the copy-swig-py
  target, for the check-swig-py target (for SWIG >= 4.0.0). this symbolic
  links are cleared on the clean-swig-py target
* Stop build with Python 3 + SWIG < 3.0.10 (or SWIG >= 4.0.0, yet)
* Stop build with Python 2 + SWIG >= 4.0.0

In subversion/bindings/swig/INSTALL:
* Add description that SWIG is optional for using distribution tarball.
* Update description of supported SWIG version.

Please review, especially I don't have any confidence in description
in INSTALL file.

Thanks,

-- 
Yasuhito FUTATSUKI <futatuki_at_poem.co.jp>