Bring workflow parameter context inline with tool.

When tool parameters are passed other_values when rendering tool forms - other_values is the context of other tools at their position in the tree, when rendering workflows other_values is the global state of the tool. The result is different handling of say parameter value filtering for tools and workflows. This changeset switches workflows/run.mako to use the same recursive calculation of context/other_values as tool_form.mako uses.
Merged in jmchilton/galaxy-central-fork-1 (pull request #349)

Bring workflow parameter context calculation in line with that of tools.