Added disable_oasis_section feature.

This feature (in alpha status) allows DisableOASISSection to be specified in the package with a list of expandable filenames given. Any generated file specified in this list doesn't get an OASIS section digest or comment headers and footers and is therefore regenerated each time oasis setup is run (and any changes made are lost).
This feature is principally intended for use with StdFiles so that, for example, INSTALL.txt and AUTHORS.txt (which often won't be modified) can have the extra comment lines removed.