Merged random-configuration checking script + few fixes

Merged random-configuration checking script + few fixes

The main Makefile has a new target - random-config - that generates
a random (but valid) configuration. This is useful for testing non-
default configurations.

The contrib/tools/random_check.sh script then further automates this
process by building random configurations multiple times.

This merge also includes several minor changes that fixed some of
the problems discovered by usage of the above mentioned script.

For the record, following configurations still do not build
(assuming the default platform profile with these alterations):

 * ARM 32 - Raspberry Pi
   * without the PL011 UART
   * with framebuffer support but without support of the BCM2835
     (this looks like a nonsense configuration that shall be
     prohibited by the configuration script itself)
 * ARM 32 - GTA-02
   * without the S3C24 UART
 * ARM 32 - Integrator/CP
   * without PC keyboard
 * PowerPC 32
   * with link-time-optimization and -Os
 * IA 32
   * when all the dynamic-linking stuff is enabled

[Merged from lp:~vojtech-horky/helenos/misc]