Fix log error message in set_last_cmdline_command

The condition on which the message is printed was inverted.
Log external command that is used to fill a menu
Add groups to custom macros
Add %A macro to the 'findprg' option

Thanks to Robert Sarkozi.
Document %A macro of the 'findprg' option
Merge branch 'add-A-macro-for-findprg'

Add %A macro to 'findprg' option, which expands to unmodified list of
arguments.

Thanks to Robert Sarkozi.