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
ruby 1.8.7 BC patch - Force encoding only for ruby 1.9
Fix deprecations and errors for SWIG 2.0.11

Extending a `struct` with its `typedef` name is deprecated as of SWIG 2.0.5.
We should use the struct name directly, even for constructors and destructors

Its not applicable for anonymous structs (of-course)
Update README for ruby 1.9.3 upgrade

*** Breaks BACKWARD COMPATIBILITY ***
as ruby 1.9.3 requires SWIG 2.0 and the latter is not
backward compatible with its older versions
Remove 1.8.7 backward compatibility patches

We are OK with ending the support with 1.8.7.
Merge pull request #27 from nnsathish/master

Upgrade Ohcount to support ruby 1.9.x