New feature for importer. rcs parser extended so that it can store parse results for quick loading in future runs. This feature has no real use in regular use of the importer, i.e. one-shot conversion of a CVS repository to fossil. It is however useful for debugging when the source repository is scanned many times during test runs. Especially for large files, with lots of changes (like ChangeLogs), the direct loading of a Tcl dictionary is much faster than actually parsing the archive files.