This fixes the path to source files in some unit tests and allows
to get rid of a few duplicate lines.

split is rendered moot by the plugin system: when enabled, binaries do
not link directly with libX11 or libGL. I hope this is a step towards
more consisteny and clarity.

and hton32() implementations everywhere instead, except in cacaserver
    which requires <arpa/inet.h> stuff anyway.

prototypes. As they are equivalent, this does not break the ABI.

<cucul.h> will provide the C99 types, even if libcaca has been installed.
  * Rename what's left of "common.h" to "stubs.h".
  * Remove all references to erroneous <inttypes.h> from source files.

* Implement strchr() in kernel.c.
  * Check for snprintf() at configure time.

kernel code.

from an alternate directory (they failed to find common.h).

in all .c files that needed it.

remove redundencies in the Doxygen documentation.

* Print a small message at kernel boot time just to check that the kernel
    was properly loaded.

as multiboot kernels.