This was broken by commit bb6b543812. Note that the original pull
request was fine, but it was broken by my own stupidity when I was
"improving" it.
The problem is that the new loadfile argument was not considered
optional anymore after my changes. The original pull request did handle
this by setting .defval to a dummy value, but I removed that part.
Fix it again by introducing a flag that designates that the parameter is
optional. (I didn't want to add it to m_option.h, because technically,
all options are optional, and it's not possible to have non-optional
options.)
MP_CMD_COMMAND_LIST commands (used to implement key bindings with
multiple commands) were not checked for abort commands. Implement it.
Remove the remarks about multi-commands being special from the manpage.
Seek coalescing is handled differently now, and the issue with abort
commands is fixed with this commit.