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'\'';'\

2 files changed, 2 insertions, 2 deletions

diff --git a/tests/mv/hard-3 b/tests/mv/hard-3
index 9a7a2a376..1a1f82fff 100755
--- a/tests/mv/hard-3
+++ b/tests/mv/hard-3
@@ -1,5 +1,5 @@
 #!/bin/sh
-# Ensure that using `cp --preserve=link' to copy hard-linked arguments
+# Ensure that using 'cp --preserve=link' to copy hard-linked arguments
 # onto existing destinations works, even when one of the link operations fails.
 
 # Copyright (C) 2003, 2006-2012 Free Software Foundation, Inc.
diff --git a/tests/mv/i-1 b/tests/mv/i-1
index 20b6ad7b9..5895137da 100755
--- a/tests/mv/i-1
+++ b/tests/mv/i-1
@@ -30,7 +30,7 @@ my @Tests =
      # Make sure a 'n' reply to 'mv -i...' aborts the move operation.
      [$test_a, '-i',
       {IN => {src => "a\n"}}, {IN => {dst => "b\n"}}, '<', {IN => "n\n"},
-      {ERR => "mv: overwrite `dst'? "},
+      {ERR => "mv: overwrite 'dst'? "},
       {POST => sub { -r 'src' or die "test $test_a failed\n"}},
       {EXIT => 0},
      ],