increment from two clients seems to not work

This was originally observed with an older version, and in trying to reproduce it the latest change seems to show incr/decr is further broken. Still, this should be an easy test to add since it's been verified to fail.

from pymembase.membaseclient import VBucketAwareMembaseClient
client_one = VBucketAwareMembaseClient('http://host/pools/default','default','')
client_two = VBucketAwareMembaseClient('http://host/pools/default','default','')

1. Client one sets a numeric key
   client_one.set('jacob',0,0,'20')
   client_one.get('jacob')

1. Client two tries to increment this numeric key
   client_two.incr('jacob')
2. This returns (0, cas) - it should be 21!
3. Client two can keep incrementing this weird key
   client_two.incr('jacob')
4. Returns (1, cas)

1. However - if client two gets the key...
   client_two.get('jacob')
   client_two.incr('jacob')
2. (21, cas)
3. !!!

p.s.: want to thank oliland from IRC on reporting this