In the Windows project generator: Switch the perl, python and ruby linkage detection to the generic library system to remove move more per project custom code.
* build.conf (libsvn_swig_py): Link to python. (libsvn_swig_perl): Link to perl. (libsvn_swig_ruby): Link to ruby. (perl, python, ruby): New external libraries.
* build/generator/gen_win.py (get_install_targets): Automatically drop swig targets based on language support. (get_linked_win_depends): Include the external libraries from swig libraries in the individual swig modules. (get_win_defines): Move the common defines to the top. Only declare HAVE_RB_ERRINFO in ruby projects. (get_win_includes): Remove language specific include handling. (get_win_lib_dirs): Remove language specific libdir handling. (get_win_libs): Remove language specific library knowledge. [python uses a Visual C++ linker trick] Suppress warnings for optional libraries when not found.