* Makefile.in (copy-swig-py:): Make symbolic links to C extension modules in build/test directory (for check-swig-py with SWIG 3.0.9 and SWIG 4.0 or later)
* build/ac-macros/swig.m4: Add SWIG version check for Python 2 and Python 3 to check its version is suitable for Python bindings, and to set up appropriate SWIG option.
Review by: hartmannathan
* subversion/bindings/swig/INSTALL (BUILDING SWIG BINDINGS FOR SVN ON UNIX, Step1): - Add description that SWIG installation is optional. - Update suitable SWIG version information per language bindings. (BUILDING SWIG BINDINGS FOR SVN ON UNIX, Step1a): Fold long line. (USING SWIG BINDINGS, Python): Update URLs for ViewVC and Trac.