Minor improvements to the regression tests (#366)

- tests/basic.sh: Fix a regression test that was failing under dtksh by
  allowing the error message to name ksh 'lt-dtksh'. Additionally, fix
  the test's inaccurate failure message (a version string is not what
  the regression test expects).

- test/builtins.sh: Exclude the expr builtin from the unrecognized
  options test because it's incompatible. Additionally, put the
  unrecognized options test inside of a function to ensure that it works
  with the future local builtin (https://github.com/ksh93/ksh/issues/123).

- tests/io.sh: The long seek test may fail to seek past the 2 GiB
  boundary on 32-bit systems, so only allow it to run on 64-bit.
  References:
  3222ac2b59/f/ksh-1.0.0-beta.1-regre-tests.patch
  a5c692e1bd

- tests/substring.sh: Add a regression test for the ${.sh.match}
  crashing bug fixed in commit 1bf1d2f8.

src/cmd/ksh93/tests/basic.sh

@@ -832,7 +832,7 @@ actual=$($SHELL --verson 2>&1)
 actual_status=$?
 expect='ksh: verson: bad option(s)'
 expect_status=2
-[[ "$actual" == ${expect}* ]] || err_exit "failed to get version string" \
+[[ "$actual" == *${expect}* ]] || err_exit "failed to handle invalid flag" \
 	"(expected $(printf %q ${expect}*), got $(printf %q "$actual"))"
 [[ $actual_status == $expect_status ]] ||
 	err_exit "wrong exit status (expected '$expect_status', got '$actual_status')"