Merge pull request #27 from bhuvi8/master

Added rsync error handling and modified WARN and ERROR functions to print to stderr
OS X compatibility and splitted rsync errors and warnings

- Fixed bug on OS X since "--" is not supported by sed.
- Changed sed to grep for consistency with rest of the code.
- Splitted handling of rsync errors/warnings - for errors we quit with
  an error code, for warnings we print a message but complete the backup
  process.