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/misc/factor b/tests/misc/factor
index d5565d66c..97da9c474 100755
--- a/tests/misc/factor
+++ b/tests/misc/factor
@@ -63,7 +63,7 @@ my @Tests =
       {EXIT => 1}],
      ['cont', 'a 4',
       {OUT => "4: 2 2\n"},
-      {ERR => "$prog: `a' is not a valid positive integer\n"},
+      {ERR => "$prog: 'a' is not a valid positive integer\n"},
       {EXIT => 1}],
     );