switching to try/except/else/finally blocks now that we no longer are constrained by python 2.4
added set and clear cancel control hook methods to task and to dispatch context
some formatting for better readability (word?)
remove prep and post sync callbacks and instead added cancel control hook via dispatch context
remove prep and post puvlish callbacks and instead added cancel control hook via dispatch context
fixed sync and publish unit tests
Merge pull request #236 from pulp/jconnor-better-control-callbacks-master

Jconnor better control callbacks master