dont_debug: ensure that $DEBUG is always restored.

Make sure that the original value of $DEBUG is
restored even if an exception is raised inside
dont_debug.
Improve debugging messages.
Never update the db if Drupid is run with --dry.
Fix uncaught exception when parsing Drush output.

Drush --format=YAML was supposed to *always*
produce a YAML structure, but if an error occurs
it just spits out an error message.
Stick with Nokogiri 1.5.9 for compatibility.

Nokogiri >=1.6.0 requires Ruby >=1.9.2.
Bump version to 1.1.3.
Add release notes for v1.1.3.