test-runner: add print_open_fds

Print opened filedescriptors when leak is detected
test-runner: print extended message when leak is detected

print how many blocks were unfreed and how many files were unclosed
when leak is detected
autotools: add m4 directory

Use m4 directory to store m4 files
wit.h: include wit-assert.h when including wit.h

to have assertf and dbg included after #include "wit.h"
configure.ac: comment on versioning
autotools: check for dependencies

Check for wayland-server/client and compilation fail when these libraries are
missing.

Also check for optional libraries, in this case for libunwind.
I wanted to split the commit with libunwind, but git add -p haven't
allowed it and I don't want to mess with it all day..
test-runner: print backtrace upon SIGSEGV

Code taken from weston.
When libunwind is present in the system, use it, otherwise use dlfcn
wit_display_destroy: don't destroy globals

display do it itself when it is being destroyed
server: close unused files after fork

When display do fork it do not need to have child's endpoints of sockets
opened.
README: update README
print_open_fds: remove type control message
test-runner: fix print_backtrace's function prototype

it took no argument but argument is of type integer.
Also change debug message accordingly
server: check if we really got SIGABRT in sigabrt handler

Honestly, it is because of the annoying warrining about unused parameter