dvtm 0.13

Updated dvtm to 0.13. Had to do a little inreplacing to work around OSX selectively removing SIGWINCH/VLNEXT in signal.h/termios.h when -D_POSIX_C_SOURCE is defined. Added a simple test.
I submitted and the author does not want to include these changes. He suggested to edit the file. Is there a better way to accomplish this than inreplace?