nova: don't wait for workers in cpu_session::pause

If a local thread is attempted to be 'pause'd via cpu_session, don't wait
until it gets into the recalled state. If the caller is lucky it is, if not
return only the stack pointer.

Avoids deadlocking of the gdb when attached to a process running a server.

Issue #478
usb: fix storage with IOMMU enabled

Fixes #747
base: make FIFO elements zero-pointer save

fix #904
hw: cancel waiting for IPC requests

ref #899
hw: kill signal receivers

ref #899
hw: fix bug in Kernel::yield_thread

ref #899
launchpad: remove '\n' from PERR message

ref #899
hw: enable multiple compilation units in kernel

ref #899
hw: enable verbose thread starts

ref #899
hw: fix bug in Kernel::Thread::resume

ref #899
hw: return error code on IPC replies

ref #899
base: fix bug in Object_pool::first_locked

fix #899