squash me to: "nova: fix cleanup handling in server object"

Issue #549
squash me - base: add remove_client to rm_session

Issue #13
base: fix sporadic context thread area faults

reverts 68156918ee5ee8150f11f5403439582dda0b9bb3
"base: apply thread.cc fix of foc to base"

Depending on the context area a fixed location is calculated where the
memory for the stack is attached to. If the context area is released before the
detach call, the very same context area can be reused and memory for the new
stack is attached for a new thread. The detach of the old thread would then
revoke the mapping for the new thread which will cause a un-handled page fault.

Issue #549
nova: kill thread with no pager where recall fails

Issue #549
base: reset pd pointer when pd session is gone

Otherwise inside the platform_thread implementation a dangling pointer is used.
Triggers during bomb test solely until now.

Issue #549
squash me to: "fix faults in rm_session de-constructor path"

don't lock dissolve of dataspace

Issue #13
nova: fix lock guard usage in cap selector

Issue #549