Don't attempt to autocorrect spelling

This frequently catches false positives for aliases, particularly for
subcommands. It also takes just as long to look at the autocorrect
prompt and select "y" as it does to just retype the command yourself.
Use default 'complete' Vim setting

Default setting is `.,w,b,u,t,i`:

* `.`: scan the current buffer ('wrapscan' is ignored)
* `w`: scan buffers from other windows
* `b`: scan other loaded buffers that are in the buffer list
* `u`: scan the unloaded buffers that are in the buffer list
* `t`: tag completion
* `i`: scan current and included files

The default setting is more likely to find a useful match, and modern
machines can search many open and unloaded buffers without pausing.