Use `id -G` rather than `groups` to get a list of groups for this

user, so that we can cope on systems like Cygwin that tend to have
group names containing spaces.

testsuite/chgrp.test

@@ -18,7 +18,9 @@ set -x
 fromdir="$scratchdir/from"
 todir="$scratchdir/to"
 
-mygrps="`groups`" || fail "Can't get groups"
+# TODO: I guess some systems will not have 'id', and therefore we have
+# to ship or emulate it.
+mygrps="`id -G`" || fail "Can't get groups"
 mkdir "$fromdir"
 
 for g in $mygrps