Version bump to v1.4.0.pre1

This is the same as pre0, but it seems like it got corrupted on its way to Rubygems.
Add support for JRuby-1.7.{5,6}

The method RubyString.encode_bang(ThreadContext) was removed, so call
the array version with an empty array instead.
Disable a lot of travis tests

Don't run 1.8-mode as it does not work with "encode!"
Don't run jruby 1.6.8 as bundler gets stuck in an endless redirect loop
Version bump to v1.4.0.pre2
Make `rake release` not confuse version tags
Twiddle around with Ruby versions

* Remove .rvmrc in favour of (private) .ruby-{version,gemset}.
* Change Travis config to run in "jruby" and only jdk7, because installing exact versions of jruby no longer works, and jdk6 isn't supported either.
Attempt to use bundler.rubygems.org directly

This should avoid endless redirect loop in bundler
Add Gemfile.lock, which changed after last commit
Compile with deprecation warnings, and remove a source of such warnings
Add .dump and .load for ActiveRecord compatibility

This closes #12
Version bump to v1.4.0
Update test cases
Add no-dependencies Java decoder

Decodes straight from bytes to JRuby objects. Old code kept for compatibility with MessagePack::Unpacker, for the time being.

Negative 64 bit integers don't work yet.
Move Unpacker to its own file
Reimplement decoder using a nio ByteBuffer
Moved the new decoder to its own class
Use Decoder#next directly from MessagePack.unpack
Update specs

* 1.0 should be packed as float 32
* Fix encoding on all strings (the file is binary so they need to be explicitly tagged as UTF-8)
* Add a string that is not UTF-8
* Fix hashes to really be as big as required to trigger the right type
Add a new Encoder that does not depend on msgpack-java
Change the "small float" example to use something with an exact representation