Instead of keeping a list of file URIs for checkpoint to flush,
open a handle and stash it.  Original references is #1114 and
Flush files in the order they were opened.
txn/txn_ckpt.c:260:33: error: 'i' may be used uninitialized in this function
Clear the count of checkpoint handles after flushing.
Merge pull request #1144 from wiredtiger/ckpt-leaf-cache-handles

Make checkpoint cache handles, not a list of URIs, when flushing leaf pages.