nova: show error message for un-handled exception

Fixes #938
Call exit handlers before notfying the parent

Fixes #941.
libports: add SDL_net

Fixes #936.
pthreads: return error numbers

pthread functions are supposed to return error values instead of setting
'errno' and returning -1.

Fixes #856.
libports: use SDL's SDL_cdrom dummy implementation

Fixes #934.
libports: use Timer_session as SDL's timer backend

A timer session is now used instead of a jiffy counter. This way, libSDL
can use a time source that is not bound to the granularity our libc's
nanosleep implementation. Currently, the granularity of nanosleep is in
the order of 10 milliseconds, which is far to coarse for the use of
SDL-using applications such as DosBox.

Fixes #934.
nova: fix size of virtual address space for 64bit

Fixes #933
noux: calculate inode value from path

There are programms that use struct stat's st_ino field to check certain
conditions. Since we are using multiple filesystems in a noux session we
cannot use the inode number which the actual filesystem provides.
Therefore we calculate a random inode number by hashing the stated path.

Fixes #299.
base-nova: Use CROSS_DEV_PREFIX in run environment

Related to #490.
qt4: Workarounds for missing C++11 compatibility

Since we switched to using C++11 by default, the webkit-related
parts of qt4 failed to compile because of C++11 compatibility
issues. This patch disables the use of C++11 for the offenders.
hw: implement priority-based scheduling (fix #945)
cpu_session: fix semantic of scale_priority

Remove "inverse" argument from function, because its documented behaviour
wasn't implemented correctly, nor was it used by any code.
Server for writing terminal output to LOG session

Fixes #947
Use log_terminal in noux.run script

This patch changes the noux.run script to use the new log_terminal
component instead of an UART driver. Besides being a nice way to test
the log_terminal service, the new version is much simpler and it just
became compatible to Linux as it no longer relies on an UART driver.

Issue #947
ports: native version of DosBox

DosBox is DOS-Emulator which is mainly used for playing old
DOS games on POSIX systems and newer Windows versions.

This port of DosBox runs natively on Genode by using its
SDL backend. It is currently only works on x86_*.

Fixes #937.
hw: remove unused function handle_invalid_syscall

ref #874
hw: remove useless function handle_invalid_excpt

ref #874
hw: header and source file for Kernel::Vm

ref #874
hw: make Kernel::mtc() global

ref #874
hw: make syscall backend private to Kernel::Thread

ref #874