Throughout change TTY_* to PTY_*, tty_* to pty_*, and ttym_* to ptmx_*.

Throughout change TTY_* to PTY_*, tty_* to pty_*, and ttym_* to ptmx_*.
* devices.cc: Regenerate.
* dtable.cc: (fh_alloc): Preserve /dev/tty name when that's what we opened.
(build_fh_pc): Preserve any existing name.
* fhandler.cc (fhandler_base::open_with_arch): Ditto.
* fhandler_tty.cc (fhandler_pty_master::fhandler_pty_master): Force the name to
/dev/ptmx while preserving other pty master device information.
* path.h (cfree_maybe): New macro.
(path_conv::operator =): Free any allocated strings in target.
(path_conv::free_strings): Delete unused function.
* sigproc.cc (proc_terminate): Remove previous accommodation for execed
processes since it didn't have the desired effect.  Change comment to a FIXME.
* spawn.cc (chExeced): Mark NO_COPY.
(exe_suffixes): Ditto.