OTWO-1206 Updates SWIG bindings to Ruby 1.9.2

- Requires SWIG 2.0.4 (SWIG 1.3 is not compatible with Ruby 1.9.2)

This updates the SWIG bindings only. This code tree does not build:

- Build fails for me when using RVM Ruby 1.9.2 because 'ruby.h' and
  'config.h' headers cannot be found. I am currenty working around
  this by manually placing absolute paths in the build script.

- test/unit/ruby/source_file_test.rb is currently failing because the
  round trip from Ruby -> C -> Ruby causes the string encoding
  metadata to be lost. UTF-8 input strings are output with identical
  content bits, but are marked as ASCII-8BIT.
OTWO-1213 Works around lost encoding in Ruby/C binding layer

When a Ruby 1.9.2 string is passed to the C code, the associated
encoding metadata is lost. When this same string is then returned from C
back to Ruby, an arbitrary, mismatched encoding is applied to replace
the lost one.

This means that a string becomes garbled in the round trip. The bits
don't change, but the encoding is lost.

The correct fix would be to preserve the encoding metadata in the C
layer.

The easier fix is to replace the lost encoding with a more likely match,
which is what I've done in this patch. When the C code returns a string,
we apply the Ruby runtime's current default encoding, which is highly likely to
be the encoding originally discarded.
Update build script to include appropriate ruby header file

* With ruby 1.9.x the location of ruby.h and config.h have changed
* This patch tries to load include the appropriate file paths while
compiling the c code based on the installed ruby version
* Tested on Ubuntu 12.04 with ruby 1.8.7 and 1.9.3
* Remove reference to the deprecated `Config` module