Release 2015.1

This is the first real feature release in two years.  In the
intervening time, there has been a *lot* of interest in Linux
containers.  However, there is to my knowledge still not another
project that achieves the same targeted feature set linux-user-chroot
has around *non-root* containers.

There are two new *opt-in* restrictions:

 - `--mount-devapi /dev`: Create just the API mount points
 - `--seccomp-profile-version 0`: Initial seccomp filtering

This release also drops support for RHEL6 era systems, and seccomp
is a hard requirement.

Git-EVTag-v0-SHA512: 3fb4a7e4c8a75004abd97133cde7bdb69ca9a6622df7601a760083bae43f278d8c266bbaa32e5fa008e806cf1854e0ec89839a1cc86a984e085f8628274bfe4d
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