These implement a new serial line interface for talking to remote
targets.
* configure.in: Link ser-hardwire.c to ser-unix.c for all hosts,
EXCEPT go32, which gets ser-go32.c.
* remote.c: Use new serial interface. More remote-xxx's to be
converted later.
* ser-bsd.c, ser-termios.c: Removed.
* serial.c: New. Implements common operations for all serial
types.
* ser-unix.c: New. Unix specific serial operations for various
flavors of Unix (Posix, SysV, BSD).
* serial.h: Generic serial interface defs.
* config/i386/go32.mh, config/i386/i386bsd.h,
config/m68k/apollo68b.mh, config/sparc/sun4os4.mh: Remove
ser-bsd.o from XDEPFILES. All the magic is now handled in
configure.in.
