bug#4280: vc-update fails under conflicts

[Glenn Morris]

Dieter Wilhelm wrote:

> When using vc-update I'm receiving the following error message in *vc*:
>
>   Conflict discovered in 'ansys-mode.el'.
>   Select: (p) postpone, (df) diff-full, (e) edit,
>           (h) help for more options: svn: Can't read stdin: End of file found

It seems that in recent versions of svn, `svn update' defaults to
offering this "interactive conflict resolution". It can be disabled by
passing the --non-interactive option to svn. This option seems to have
been first added to svn in 2002, so it's probably fine to use this
unconditionally in vc-svn.el.