bug#19045: 25.0.50; [PATCH] vc-git-print-log use --follow

[Juri Linkov]

>> In the command line of git version 1.9.1 running git log on two files
>> (command line copied from *Messages* when vc-command-messages is t)
>> 
>>   git --no-pager log --no-color --follow -n 2000 -- vc-dispatcher.el 
>> vc-git.el
>> 
>> fails with the error:
>> 
>>   usage: git logs can only follow renames on one pathname at a time
>> 
>> whereas running git on one directory ‘vc’
>> 
>>   git --no-pager log --no-color --follow -n 2000 -- vc
>> 
>> doesn't fail.  Although I can't confirm the correctness of the output log:
>> it seems the option ‘--follow’ has no effect on directories.
>
> Even if it's true, it means --follow doesn't do any harm when invoked
> on directories, and we shouldn't disallow that.

I don't know the reason why disallowing directories was implemented
in the first place.  Maybe ‘git log --follow’ failed on directories
in some older git versions?  Wouldn't it be safer to leave the code
that checks for directories and doesn't add ‘--follow’ for this case?