Added a changelog entry for the 0.3.0 release
Removed the default handlers for all commands

This commit replaces the removed handlers with conditionally-enabled ones
defined in the org.eclipse.ui.handlers extension point
Register Java proof action handlers with the workbench handler service

Now that there are no default handlers to conflict with, this change allows
the Java handlers to keep working when focus shifts to a different view
Added wrappers for all of the MessageDialog dialogs to UIUtils

This commit also removes the mandatory call to UI.syncExec, so callers
should take care to invoke these wrappers from the UI thread
Prompt the user to fix the Coq preferences if initialisation fails
Perform quality control in the CoqTopIdeSlave_v20120710 instance factory

The factory now attempts to call the CoqTopIdeSlave_v20120710.about method
before it returns anything
Discard any exceptions thrown by the JobRunner.finish method
Modified the CoqStepForwardJob.initialise method to catch all exceptions

This allows coqtop creation failures to be reported properly to the user
Prompt the user to save the proof certificate when a Java proof is complete
Print Coq messages to the Eclipse console

This commit restores behaviour that was lost in the move to ideslave, and
makes commands like Check and Eval work properly again