Do not add bogus line to apt preference file on Debian Wheezy
Remove the preference file for all supported platforms when in purge mode
Updated readme to indicate danger of setting preference purge options
Testing if we are not touching the preference file when purge mode is off
Fixed acceptance spec and add debian nodeset
Some code cleaning
Add dpaulus to the contributors list
Merge pull request #290 from dpnl87/wheezy-preference-fix

Do not add bogus line to apt preference file on Debian Wheezy