base: extend thread test for stack alignment
os: handle ipc error in server framework

When using the server framework, it might happen that the main thread
tries to forward a signal to the entrypoint, while the context of that
signal is already destroyed. In that case the main thread will get an
ipc error exception as result.

Related to #113
block: cache between one client and one device

This block cache component acts as a block device for a single client.
It uses fixed 4K blocks as caching granularity, thereby implicitly reads
ahead whenever a client requests lesser amount of blocks. Currently,
it only supports a least-recently-used replacement policy.

Fixes #113
block: prevent from dereferencing invalid pointers

Until now, block drivers had to deal with a pointer to the client
session component, e.g.: to acknowledge block packets already processed.
When a session was closed, the driver object wasn't informed explicitly,
which leads to defensive programming, or lastly to a race-condition in
test-blk-srv. To prevent from this class of errors, the pointer is now
private to the generic block driver base class, and not accessible to
the concrete driver implementation. Moreover, the driver gets explicitly
informed when a session got invalidated.

Ref #113
hw: ease usage of the kernel log

ref #989
hw: use descriptive bool value names in ipc.cc

ref #989
hw: fix bug in IPC message-size calculation

ref #989
core: change policy incrementation to prefix op

Using prefix incrementation makes sure a policy with id == 0 is
invalid.

Fixes #1049.
os: initial version of trace_fs

The trace_fs server provides access to a Trace_session by using a
File_system_session as frontend.

Each trace subject is represented by a directory ('thread_name.subject')
that contains specific files ('active', 'cleanup', 'enable', 'events',
'buffer_size' and 'policy'), which are used to control the tracing
process of the thread as well as storing the content of its trace
buffer.

The tracing of a thread is only activated if there is a valid policy
installed and the intend to trace the subject was made clear by writing
'1' to the 'enable' file.

The tracing of a thread may be deactived by writing a '0' to the
'enable' file.

A policy may be changed by overwriting the currently used one. In this
case the old policy is replaced by the new policy and is automatically
utilize.

Writing a value to the 'buffer_size' file changes the appointed size of
the trace buffer. This value is only evaluted by reactivating the
tracing process.

The content of the trace buffer may be accessed by reading from the
'events' file. Throughout all tracing session new trace events are
appended to this file.

Nodes of UNTRACED subjects are kept as long as they do not change their
tracing state to DEAD. In this case all nodes are removed from the
file system. Subjects that were traced before and are now UNTRACED will
only be removed by writing '1' to the 'cleanup' file - even if they
are DEAD by now.

To use the trace_fs a config similar to the following may be used:

! <start name="trace_fs">
! 	<resource name="RAM" quantum="128M"/>
! 	<provides><service name="File_system"/></provides>
! 	<config>
! 		<policy label="noux -> trace" interval="1000" subject_limit="512" trace_quota="64M" />
! 	</config>
! </start>

'interval' sets the periode in which the Trace_session is polled. The
time is given in milliseconds.
'subject_limit' speficies how many trace subject should by acquired at
most when the Trace_session is polled.
'trace_quota' is the amount of quota the trace_fs should use for the
Trace_session connection. The remaing amount of RAM quota will be used
for the actual nodes of the file system and the 'policy' as well as the
'events' files.
In addiition there are 'buffer_size' and 'buffer_size_limit' that define
the initial and the upper limit of the size of a trace buffer.
Tracing of parent processes or rather threads may be enabled by setting
'parent_levels' to a value greater than '0' (though this attribute is
available, the trace session component within core still lacks support
for it).

A ready-to-use runscript can by found in 'ports/run/noux_trace_fs.run'.

Fixes #1049.
Fix several format string warnings
base: Add 'construct_at' utility

This utility allows for the manual placement of objects without the need
to have a global placement new operation nor the need for type-specific
new operators.

Issue #989
d3m: Fix deadlock of usb_drv

This deadlock was introduced by the change of USB driver to the server
API.

Fixes #1052
iso9660: Increase entrypoint stack size for 64bit
d3m: Adaptation to USB driver config change
d3m: quota adjustment for ps2 driver
liquid_fb: Fix decoration config option

The decoration configuration is used by Qt5 to omit window decorations
from menus. It got lost during the restructuring of the scout widgets.
News item for FOSDEM slides
Qt5: reserve screen space for the liquid_fb title bar

With this patch, the liquid_fb title bar height gets reserved at the top of the
screen, so if a Qt application wants to position a window at (0,0), there's
still enough space to show the title bar above.

Issue #1054.
tool_chain: check for various autoconf installs.

There exist different default setups for a specific autoconf version:
* autoconf
* autoconf$(VERSION)
* autoconf-$(VERSION)

As of now, only the second option is recognized by the check in tool_chain.

This patch ensures that if one of those is present in the correct
version, it will be found and used in the build process.

Fixes #1053.
base: optional length argument for String::String