remote-hms.c, remote-mm.c, remote-nindy.c, remote-vx.c, remote.c,
target.c, target.h, valarith.c, valops.c, value.h, xcoffexec.c:
Remove to_call_function and target_call_function, since it
always calls the same thing (call_function_by_hand).
target.c: Add target_preopen and target_command.
Remove target_info.
(add_target): Call add_cmd and mess with targetlist->doc.
core.c, exec.c, remote-eb.c, remote-nindy.c, remote-vx.c,
remote-vx.68.c, inftarg.c, remote.c: Add doc field to target struct.
Call target_preopen from open routine.