libports: add jitterentropy-20140411

This commit adds a port the jitterentropy library to Genode. As
backend on x86_{32,64} 'rdtsc' is used and on ARMv{6,7} the
performance-counter.

Fixes #1239.
libports: add vfs_jitterentropy library

This file system library uses the the jitterentropy library to provide
a rudimentary '/dev/random' device.

Fixes #1239.
libc: add if_tun.h

Fixes #1235.
ports: add openvpn-2.3.4

The port was succesfully tested a echo test and lighttpd. DHCP over
OpenVPN is not tested and probably will not work out of the box.
Therefore, the ip address etc. need to be specified manually.

For now, only ethernet bridging (using a TAP device) is supported.

Fixes #1235.
libc: add net/route.h and its dependencies

Fixes #1235.
nit_fb: fix translation of absolute motion events
decorator: redraw after disappearing window
nitpicker: fix find_view w/o pointer present

Before the pointer handling was removed from the nitpicker server, the
pointer was always the first view, which was skipped in the find_view
function. However, since we support pointer-less operation by now, we
have to consider all views starting with the top-most one.
demo.run: adapt nested nitpicker to config changes
wm.run: use priorities for smoother rpi GUI