Re: [PATCH 2/3] completion: extract completing ctags symbol names into helper function

> The previous commit doubled the number of __git_match_ctag()'s
> positional parameters, and, to keep the position of existing
> parameters for the sake of backwards compatibility, the prefix,
> current word and suffix parameters ended up in different order than in
> other functions accepting the same parameters.  Then there is a
> condition checking the existence of the tag file before invoking this
> function.
> 
> We could still live with this if there were only a single callsite,
> but the next commit will add a few more, so it's worth providing a
> cleaner interface.
> 
> Add the wrapper function __git_complete_symbol(), which encompasses
> the condition for checking the presence of the tag file and filling
> COMPREPLY, and accepts '--opt=val'-style options with default values
> that keep callsites simpler.