Remove Gemfile.lock from version control.

It should not be under version control in a gem:

http://yehudakatz.com/2010/12/16/clarifying-the-roles-of-the-gemspec-and-gemfile/
Update .gitignore

The ignore list is copied from a fresh result of a
“bundler gem“ command.
Use activemqcpp-config for finding the compilation flags
Chomp and pad activemqcpp-config output
Limit rspec version to 2.x
Load the version explicitly
Remove ruby-debug (for now?)
Expect Module#constants to return Symbols

This breaks Ruby 1.8 compatibility.
Stop using #be_true and #be_false expectations
Implement broker_url using {get|set}BrokerURI

getBrokerURL and setBrokerURL seem to be removed, so
we'll use the string version of setBrokerURI and a tiny wrapper
around getBrokerURI to implement #broker_url.