rx: Rework identity copying

rx: Rework identity copying

Change the behaviour of the rx_identity_copy function so that it
copies the whole identity, not just the contents. Add a new function
rx_identity_copyContents which just copies the contents of an identity
into an existing identity structure.

This restores symmetry with the free and freeContents functions.

Change-Id: I692ac8434b1538c283a8ae713956be8ae67cccfd
Reviewed-on: http://gerrit.openafs.org/3352
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Jeffrey Altman <jaltman@openafs.org>