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, 2 insertions, 2 deletions

diff --git a/tests/check.mk b/tests/check.mk
index b66e6a3ed..cb67b9dde 100644
--- a/tests/check.mk
+++ b/tests/check.mk
@@ -44,11 +44,11 @@ check-am: .built-programs
             && MAKEFLAGS= $(MAKE) -s built_programs.list)		\
           > $@-t && mv $@-t $@
 
-## `$f' is set by the Automake-generated test harness to the path of the
+## '$f' is set by the Automake-generated test harness to the path of the
 ## current test script stripped of VPATH components, and is used by the
 ## shell-or-perl script to determine the name of the temporary files to be
 ## used.  Note that $f is a shell variable, not a make macro, so the use of
-## `$$f' below is correct, and not a typo.
+## '$$f' below is correct, and not a typo.
 LOG_COMPILER = \
   $(SHELL) $(srcdir)/shell-or-perl \
   --test-name "$$f" --srcdir '$(srcdir)' \