bug#29303: 25.2; vc-git-grep should shell-escape FILES

[Eli Zaretskii]

> From: Robert Pluim <rpluim@gmail.com>
> Cc: 29303@debbugs.gnu.org,  gus@inodes.org
> Date: Wed, 15 Nov 2017 21:17:35 +0100
> 
> > That's okay portability-wise, but why do you need split-string?
> > AFAIU, grep-read-files reads a single pattern, no?
> 
> grep-read-files has support for grep-files-aliases which allows you to
> eg say 'cc' and have it expand to "*.cc *.cxx *.cpp *.C *.CC *.c++"

Ah.  So we lose support of patterns with embedded whitespace in order
to support the aliases?  Is that desirable?