Remove dead code in emark_cmd()
Fix style of comments in commands_completion.h

Make them start with a capital letter and end with a dot.
Add empty lines to commands_completion.h
Update fast_run_complete() declaration

Add a comment and replace  * with [] in arguments list.
Use format_str() in fast_run_complete()
Don't fastcomplete absolute paths

Thanks to MadMaverick9.
Rename exec_completion -> complete_command_name

Also rename the only parameter from str to beginning.
Update style of comments in engine/completion.h
Add completion_groups_unite()
Add unit-tests for completion_groups_unite()
Extract group_unique_sort() in engine/completion.c

Sorts items of the list in range [start_index, start_index + len)
with de-duplication.  Updates number of list elements and next
group beginning.
Remove all duplicates from fastrun completion list

Fixes running external commands with 'fastrun' option set, in case when
there are more than one executable with given name.
Merge branch 'fix-fastrun-by-full-path'

Fix two issues with running external commands when'fastrun' option is
set.