QPID-4495: RVM fails to use C++ compiler for the Ruby gem.

mkmf tries to find a basic working compiler and linker first, and when
it finds gcc it stops. But since Qpid is written in C++ this causes the
gem to fail to install when the C++ libraries checked.

This fix forces mkmf from the outset to use a C++ compiler instead.
Bumped the gem version to 0.18.2
JIRA 4291 : Some cleanup on the rdoc generation and markups.

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1397260 13f79535-47bb-0310-9956-ffa450edef68
JIRA 4291 : Renamed the gemfile to qpid_messaging.

Updated the examples and libraries to reflect this change.

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1397261 13f79535-47bb-0310-9956-ffa450edef68
JIRA 4291 : Consolidated all requires in Ruby library.

Previously each library file was requiring 'cqpid'. Moved this into the
lib/qpid_messaging.rb file.

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1397262 13f79535-47bb-0310-9956-ffa450edef68
Bumped the release to 0.18.3.