We have to clean out the table of appended keys after each run, otherwise
it eventually fills up and we never insert another record.  Rework append
table processing to be more resiliant, ignore the append table entirely in
the case of row-store objects.
lint: Warning 550: Symbol 'nsnapshot' (line 167) not accessed
Retry open_cursor if data source is locked.
Merge branch 'develop' of github.com:wiredtiger/wiredtiger into develop