build: Drop vars used to build multiple binaries

manual: readline is not used anymore

load_trakc/smf_gettrack: Don't access device if event has no device

Fixes crashes

Properly ignore nested notes instead of aborting.

If after the filter layer there's a nested note (eg the same note is
played simultaneously on two keyboards and routed to the same output)
just ignore it.

Found by bang corrupt <[email protected]>, thanks!

s/function/command/

Implement undo for iset and oset.

test for CLOCK_MONOTONIC on OSX, as new releases have clock_gettime

mdep_mux_wait() calls itself from blocking r and p commands (in batch

mode). But if the inner mdep_mux_wait() call gets input, the
interpreter is called to process statements after the 'r' and 'p'
commands, which in turn end-up not being blocking. Found
by Michael W. Bombardieri <mb at ii.net>.

Fix tty code to submit all the input (not the last line only). Fixes

plain files being mis-interpreted. Found by Luc Tanguay <lucus
at sympatico.ca>, thanks.

When the song is relocated, check if the end of the project is

reached and if so, don't start playback in batch mode.
This avoids the dalay between the start event and the first
clock tick which trigger an active sensing message. Problem
found by Luc Tanguay <lucus at sympatico.ca>