Cannot install due to AttributeError: LCB_SUBDOC_MULTI_FAILURE

I tried to install couchbase-2.2.2 and couchbase-python-cffi@2.x in my PyPy environment. But the installation was failed due to an error:

```
$ pip install couchbase
Collecting couchbase
Using cached couchbase-2.2.2.tar.gz
Installing collected packages: couchbase
Running setup.py install for couchbase ... done
Successfully installed couchbase-2.2.2
You are using pip version 8.1.2, however version 9.0.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.

$ cd ~/couchbase-python-cffi
$ python setup.py install
Traceback (most recent call last):
File "setup.py", line 2, in
import couchbase_ffi._cinit
File "/home/sub/works/couchbase-python-cffi/couchbase_ffi/__init__.py", line 51, in
_libcouchbase._stage2_bootstrap()
File "/home/sub/works/couchbase-python-cffi/couchbase_ffi/_libcouchbase.py", line 78, in _stage2_bootstrap
from couchbase_ffi.bucket import Bucket
File "/home/sub/works/couchbase-python-cffi/couchbase_ffi/bucket.py", line 18, in
import couchbase_ffi.executors as executors
File "/home/sub/works/couchbase-python-cffi/couchbase_ffi/executors.py", line 4, in
from couchbase.exceptions import ValueFormatError, ArgumentError, CouchbaseError
File "/home/sub/env-pypy/site-packages/couchbase/exceptions.py", line 507, in
class SubdocMultipleErrors(CouchbaseError):
File "/home/sub/env-pypy/site-packages/couchbase/exceptions.py", line 509, in SubdocMultipleErrors
CODE = C.LCB_SUBDOC_MULTI_FAILURE
File "/home/sub/works/couchbase-python-cffi/couchbase_ffi/__init__.py", line 46, in __getattr__
raise AttributeError(item)
AttributeError: LCB_SUBDOC_MULTI_FAILURE
```

My PyPy environment is:

```
Python 2.7.10 (5.0.1+dfsg-4, Apr 08 2016, 00:22:14)
[PyPy 5.0.1 with GCC 5.3.1 20160407]
```

Inizia riproducendo `python setup.py install` nell’ambiente PyPy indicato. Ispeziona `couchbase_ffi/__init__.py`, in particolare `__getattr__`, e il riferimento a `LCB_SUBDOC_MULTI_FAILURE` in `couchbase/exceptions.py`. È completato quando il package si installa senza questo AttributeError nell’ambiente indicato.

Scritto dal modello di indicizzazione a partire dal testo della issue.