Display error message when strace is not available.

Mark autogen.sh executable in svn.

TraceScreen.c

@@ -77,6 +77,8 @@ void TraceScreen_run(TraceScreen* this) {
       fcntl(fdpair[1], F_SETFL, O_NONBLOCK);
       sprintf(buffer, "%d", this->process->pid);
       execlp("strace", "strace", "-p", buffer, NULL);
+      const char* message = "Could not execute 'strace'. Please make sure it is available in your $PATH.";
+      write(fdpair[1], message, strlen(message));
       exit(1);
    }
    fcntl(fdpair[0], F_SETFL, O_NONBLOCK);