added dump method to lib/VCP/DB_File/sdbm.pm to dump keys => values
from a sdbm file. removed similar code from bin/dump_head_revs,
bin/dump_rev_map and bin/dump_main_branch_id and called this method
instead. also made parse_files_and_revids_from_head_revs_db sub
in TestUtils to use in test suites instead of
parse_files_and_revids_from_p4_files et. al.