Revert "PCBC-227: Allow store of pure numeric keys"

This patch breaks PCBC-191

This reverts commit 8382d3321bc09d8a5ecdba2c3726f65998ba2664.

Change-Id: Iafd740c6594d9cb31654226cfafb938e3728a2e4
Reviewed-on: http://review.couchbase.org/26223
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>