(PUP-1044) Make FileBucket::File use a local file whenever possible
(PUP-1044) Add info output for when file/string is used for checksum

This commit adds Puppet.info calls to make it possible to monitor the
number of file vs string checksum computations  They can be ovserved
when running in verbose mode.
(PUP-1044) Cleanup commented out code, and comments
(PUP-1044) Fix missing file mode in call to file system open

The mode 'nil' was accidentally dropped in the call to open the
file to get a stream. This caused 9 tests to fail.
(PUP-1044) Replace IO::copy_stream with FileUtils.copy_stream for 1.8.7

Ruby 1.8.7 does not have IO::copy_stream, this method is only available
on FileUtils.
Merge pull request #2982 from hlindberg/PUP-1044_filebucket-less-memory

(PUP-1044) Make FileBucket::File use a file when possible