Binding 'repeat' (DOAGAIN, or redo) to a different key than ^A
didn't work as intended because the code that used it was
checking for DOAGAIN (a key value from config.h) instead of
g.Cmd.spkeys[NHKF_DOAGAIN] (the key currently bound to repeat).
Contrary to the github issue, re-bound prefix keys worked ok for
me if followed by a direction. However, they behaved strangely
if followed by anything else. If the keystroke was stolen from
some other command and that command hadn't been bound to another
key, following the prefix with a non-direction could end up
executing the command that used to own the key. For example,
BIND=d:nopickup
to use 'd' to move without auto-pickup would work if you used
d<direction> but if you used d<something-else> if would execute
the drop command.
The NHKF_REQMENU prefix could be bound to some key other than
'm' but it only worked as intended if the new key was a movement
prefix.
This also makes DOAGAIN be unconditional. If it is deleted or
commented out in config.h, the default binding will be '\000' so
unusable (freeing up ^A for something), but still be available
to be bound to some key (perhaps even ^A).
This also includes an unrelated change to mdlib.c. The comments
added to config.h will force a full rebuild. Changing mdlib.c
now rather than separately will avoid forcing that twice.
Fixes#426