tests: more automated quote adjustment

Relax initial regexp to match more instances, but add a
filter to avoid some invalid conversions.  Run this:

git grep -l "\`[^']*'" tests | xargs perl -pi -e '$q=q"'\''";' \
  -e '$q="$q\\$q$q"; /(= ?\`|\`expr|\`echo|\Q$q\E)/ and next;' \
  -e ' s/\`([^'\''"]*?'\'')/'\''$1/g'
The last disjunct in the above (...) filter is to exempt
any line that contains this string: '\''
With quoting like that, converting a ` to ' is likely to cause trouble,
so we'll handle those manually.  Here are three examples where
the exemption is required:

  *': `link-to-dir/'\'': hard link not allowed for directory'*) ;;
  printf 'creating file `%s'\''\n' $f
  'mv: inter-device move failed: `%s'\'' to `%s'\'';'\

1 files changed, 1 insertions, 1 deletions

diff --git a/tests/chgrp/deref b/tests/chgrp/deref
index cf1ddd869..dcdc4367a 100755
--- a/tests/chgrp/deref
+++ b/tests/chgrp/deref
@@ -52,7 +52,7 @@ set _ `ls -ln f`; g=$5; test "$g" = $g2 || fail=1
 
 # This *should* change the group of f.
 # Though note that the diagnostic you'd get with -c is misleading in that
-# it says the 'group of `symlink'' has been changed.
+# it says the 'group of 'symlink'' has been changed.
 chgrp --dereference $g1 symlink
 set _ `ls -ln f`; g=$5; test "$g" = $g1 || fail=1
 set _ `ls -ln symlink`; g=$5; test "$g" = $g2 || fail=1