A holiday tradition continued Saturday night in Mont Clare.   Volunteers lined the banks of the Schuylkill Canal with about a thousand luminary bags.   They cast an eerie glow on the water and lit the path that runs almost a mile between Route 29 and the old locktender's house.   The Schuylkill Canal Association decorated the historic house in the fashion of the early 19th century, the heyday of commerce on the canal when barges carried farm crops and coal down the waterway into Philadelphia.   The canal is now part of a Montgomery County park and association officials hope the proposed budget cuts at the county level don't have much of an impact on the historic site.   The holiday open house is a tradition that started almost three decades ago as the Schuylkill Canal Association began the restoration of the 184-year-old qaterway and the historic structures nearby.