Allow using attribute 'optional' for data column parameters.
For consistency with other parameters, has the opposite effect of 'force_select'.
Merged in jmchilton/galaxy-central-fork-1 (pull request #575)

Allow using attribute 'optional' for data column parameters.
Sanitize workflow and input dataset names in workflow run.mako.
Sanitize display of workflow parameters in workflow run.mako.
Sanitize workflow run.mako parameters not sanitized by tooling code.
More sanitization in workflow display.mako.
Sanitize workflow name in message when extracting workflow from history.
Sanitize workflow name in myexperiment export.

On the off chance that XML file ever gets interpreted as HTML. Shouldn't hurt anything for well behaved workflow names.
Sanitize tool id, name, and version during workflow import.
More sanitization while handling fields from an imported workflow.
More sanitizing of workflow name and tool information during import.
Sanitize workflow name and tool ids when running workflow with missing tools.
Sanitize incoming workflow annotations during imports.
More workflow template sanitization during rename, copy, delete.
Sanitize all values in configure_menu.mako.
Sanitize workflow names in tool menu.
Sanitize workflow and dataset names in run_complete.mako.
Sanitize values in switching data parameter form.
Sanitization for workflows_for_run.mako.
Remove seemingly unused message cruft in workflow list_for_run.mako.