Only 4.4 clusters will support the allowDiskUse option for external sort with the find command. However, in order to allow old shells to be forwards compatible with a 4.4 cluster, we may wish to backport shell support for the allowDiskUse() helper. This helper was implemented in a 4.3 development version under SERVER-42077, which also made changes to mongod. This ticket tracks the work to separate the shell work from the remainder of the commit for SERVER-42077, and apply these changes to the 4.2 branch.