Following up on r1412632, fix name of new svn_wc__db_ function and use this function for all calculations on where to obtain a working copy lock.
* subversion/libsvn_wc/lock.c (child_is_disjoint): Simplify function by using svn_wc__db_is_switched(). (svn_wc__acquire_write_lock): Use svn_wc__db_is_switched() instead of all the separate db calls. Remove tests on cases that could never happen since the switch to a single database per working copy.
* subversion/libsvn_wc/lock.c (svn_wc__internal_check_wc): Don't error out on WCs that now aren't auto-upgraded anymore. Treat them the same as missing and unsupported WCs to allow checkout of nested working copies within such WCs. Fixes the bulk of the test suite failures I introduced in r1404856 if the tests are run within a 1.7 format working copy.