feature: comment current line if no region is marked for comment-or-uncommnet-region command.

[sakurawald]

The command comment-region will comment current line if there is no region marked. (In other words, it's now in vi-normal mode.)

However, the command comment-or-uncomment-region will not comment current line if there is no region marked. This is annoy, if i only want to comment 1 single-line, i have to switch to vi-visual mode, and use comment-or-uncomment-region, and switch back to vi-normal mode.

This is also the same in case you want to un-comment a single-line.