cgroups: support for MemoryAndSwapLimit= setting

Add a MemoryAndSwapLimit setting that behaves the same way
as MemoryLimit, except that it controls the
memory.memsw.limit_in_bytes cgroup attribute.
cgroups: support for KernelMemoryLimit= setting

Add a KernelMemoryLimit setting that behaves the same way
as MemoryLimit, except that it controls the
memory.kmem.limit_in_bytes cgroup attribute.
cgroups: support for MemorySoftLimit= setting

Add a MemorySoftLimit setting that behaves the same way
as MemoryLimit, except that it controls the
memory.soft_limit_in_bytes cgroup attribute.
cgroups: support for KernelTcpMemoryLimit= setting

Add a KernelTcpMemoryLimit setting that behaves the same way
as KernelMemoryLimit, except that it controls the
memory.kmem.tcp.limit_in_bytes cgroup attribute.