Backport ksh93v- regression tests and fix various regression test bugs (#472)

- tests/*.sh: Backported many additional regression tests and test
  fixes from the alpha and beta releases of ksh93v-.

- tests/alias.sh: Avoid trying to add vi to the hash table, as some
  platforms do not provide a vi(1) implementation installed as part
  of the default system. This fixes a regression test failure I was
  getting in one of my Linux virtual machines.

- tests/builtins.sh: Fixed a bug in one of the regression tests that
  caused an incorrect total error count if any of the tests failed.

- tests/sh_match.sh: Fixed a regression test failure on DragonFly
  BSD caused by the diff command printing an extra 'No differences
  encountered' line.

src/cmd/ksh93/tests/variables.sh

@@ -561,6 +561,10 @@ actual=$*
 [[ $actual == "$expect" ]] || err_exit "IFS failed with invalid multi-byte character" \
 	"(expected $(printf %q "$expect"), got $(printf %q "$actual"))"
 
+# Backported test from ksh93v- 2013-06-28 for 'unset IFS'
+unset IFS
+[[ ${IFS+abc} ]] && err_exit "testing for unset IFS not working"
+
 # ^^^ end: IFS tests ^^^
 # restore default split:
 unset IFS