cbbackup creates incorrect directory structure when empty buckets precede non-empty buckets alphabetically

Actually affects 3.0.1 release but that version is not available for selection.

To reproduce:

• Start a new Couchbase 3.0.1 node.
• Configure the node and load the beer-sample bucket, and also create the default bucket.
• Run cbbackup as shown below in the first example to obtain one directory structure.
• Delete the default bucket and create a new bucket named "a_bucket", containing no items.
• Run cbbackup as shown in the second example to obtain the other directory structure.

Example 1:
$mkdir -p ~/backuptest/example1

$./cbbackup -u Administrator -p couchbase -m accu -v http://127.0.0.1:8091 ~/backuptest/example1

$cd ~/backuptest/example1

$find .
.
./2014-11-03T185815Z
./2014-11-03T185815Z/2014-11-03T185815Z-full
./2014-11-03T185815Z/2014-11-03T185815Z-full/bucket-beer-sample
./2014-11-03T185815Z/2014-11-03T185815Z-full/bucket-beer-sample/design.json
./2014-11-03T185815Z/2014-11-03T185815Z-full/bucket-beer-sample/node-127.0.0.1%3A8091
./2014-11-03T185815Z/2014-11-03T185815Z-full/bucket-beer-sample/node-127.0.0.1%3A8091/data-0000.cbb
./2014-11-03T185815Z/2014-11-03T185815Z-full/bucket-beer-sample/node-127.0.0.1%3A8091/failover.json
./2014-11-03T185815Z/2014-11-03T185815Z-full/bucket-beer-sample/node-127.0.0.1%3A8091/meta.json
./2014-11-03T185815Z/2014-11-03T185815Z-full/bucket-beer-sample/node-127.0.0.1%3A8091/seqno.json
./2014-11-03T185815Z/2014-11-03T185815Z-full/bucket-beer-sample/node-127.0.0.1%3A8091/snapshot_markers.json
./2014-11-03T185815Z/2014-11-03T185815Z-full/bucket-notdefault
./2014-11-03T185815Z/2014-11-03T185815Z-full/bucket-notdefault/design.json

Example 2:
$mkdir -p ~/backuptest/example2

$./cbbackup -u Administrator -p couchbase -m accu -v http://127.0.0.1:8091 ~/backuptest/example2

$ cd ~/backuptest/example2

$find .
.
./bucket-a_bucket
./bucket-a_bucket/2014-11-03T215924Z-full
./bucket-a_bucket/2014-11-03T215924Z-full/bucket-beer-sample
./bucket-a_bucket/2014-11-03T215924Z-full/bucket-beer-sample/design.json
./bucket-a_bucket/2014-11-03T215924Z-full/bucket-beer-sample/node-127.0.0.1%3A8091
./bucket-a_bucket/2014-11-03T215924Z-full/bucket-beer-sample/node-127.0.0.1%3A8091/data-0000.cbb
./bucket-a_bucket/2014-11-03T215924Z-full/bucket-beer-sample/node-127.0.0.1%3A8091/failover.json
./bucket-a_bucket/2014-11-03T215924Z-full/bucket-beer-sample/node-127.0.0.1%3A8091/meta.json
./bucket-a_bucket/2014-11-03T215924Z-full/bucket-beer-sample/node-127.0.0.1%3A8091/seqno.json
./bucket-a_bucket/2014-11-03T215924Z-full/bucket-beer-sample/node-127.0.0.1%3A8091/snapshot_markers.json
./bucket-a_bucket/design.json