setting a new value for an expired item before the pager cleans up the value from memory causes memory leak

this can cause a huge memory spike
example

while True:
mc.set(key,1,0,..)

we do not overwrite the value in kv table because expiration is less than 3 so for every set we end up creating a new value in the kv table

this is not a real use case but is seen very often while testing ( e.g a script sent by one of the customers was causing this issue)

for example if you have a working set of 4000 keys ( data 400 mb) and you loop 400 times and invoke a mc.set(key,2,..) after 10 minutes you will end up with 4x400Mb