Clean up depth handling in debug output

Clean up depth handling in debug output

The indentation shown in debug output was misleading.  Increment the
depth when we are working on a prerequisite, not for the current
target.

* src/remake.c (check_dep): Increment depth only on recursion.
(update_file_1): Ditto.  Don't show "Finished..." if prereqs are
still running.
* src/implicit.c (pattern_search): Increment depth for the entire
search.
* tests/scripts/features/output-sync: Support debug output when run
by hand.