Merge python-bindings-improvements to trunk, by comparing trunkURL with branchURL.
Major changes: * Always build SWIG headers in the build dir, unless we are still using pristine SWIG headers from an official Subversion release (r15865). * Enable SWIG bindings, even if we compile --without-swig. In release builds, we can build the bindings without SWIG (r15857). * Refactor SWIG generator to use a modular architecture, separate from the Unix / Windows generators (r15855).
Minor changes: * See r15879, r15870, r15868, r15867, r15857, and r15856.