Added Buildr 'Buildfile' and 'buildfile'

All other options (as listed at https://github.com/apache/buildr/blob/master/lib/buildr/core/application.rb#L110) are already covered by other things here.
Towards testing for presence of sample files
Removing pry
Adding debugging for failed assertions
Adding all_extensions method to Language
Adding Common Lisp examples with .cl extension
Removing .cu extension for Cirru (unable to find examples in the wild)
Adding pod example for Perl
Adding R example with .r extension
Adding .pluginspec example for XML
Regenerating samples.json
Removing extra `.`
Merge pull request #1110 from github/samples_checking

Towards testing for presence of sample files
Merge pull request #1060 from kohenkatz/patch-1

Added Buildr 'Buildfile' and 'buildfile'