cuahsi/wof enhancements

Addressed Issue #64 (very simple change). Also Issue #60: Upgraded cuahsi/wof services to re-use a suds client instance if already opened, and allow an optional suds cache argument. Did some testing (issued WOF requests) to make sure wof requests worked w/o the new suds_cache argument (ie, use default; same API behavior as before), as well as with suds_cache=None. Did not check the actual cache behavior on local /tmp directory.