gh-475: Fix issues in third_party/proctitle.c

 * add proctitle.h;
 * add config-time detection of setproctitle() syscall;
 * fixing program_invocation_(short)?_name globals (glibc);
 * fixing progname (getprogname(), initialized with argv[0]);
 * this module now works on osx;
 * fix osx ps displaying garbage (argc-1 extra \0 necessary);
 * general refactoring;
 * fix linux proctitle truncation (init_set_proctitle was called with
   argv+1, this is wrong);

 * CAVEAT: 'progname: ' prefix no longer present, will fix later