Memory leak(s) when modifying PATH in various contexts

[McDutchie]

These regression tests leak:

ksh/src/cmd/ksh93/tests/leaks.sh

Lines 355 to 368 in 5422af4

	TEST title='set PATH attribute in main shell' known=y url=https://github.com/ksh93/ksh/issues/405
	DO
	typeset -A PATH
	unset PATH
	PATH=$save_PATH
	hash "${random_utils[@]}"
	DONE
	TEST title='unset PATH in main shell' known=y url=https://github.com/ksh93/ksh/issues/405
	DO
	unset PATH
	PATH=$save_PATH
	hash "${random_utils[@]}"
	DONE

ksh/src/cmd/ksh93/tests/leaks.sh

Lines 376 to 394 in 5422af4

	TEST title='set PATH value in subshell' known=y url=https://github.com/ksh93/ksh/issues/405
	DO
	(PATH=/dev/null)
	DONE
	TEST title='run command with preceding PATH assignment in subshell' known=y url=https://github.com/ksh93/ksh/issues/405
	DO
	(PATH=/dev/null command true)
	DONE
	TEST title='set PATH attribute in subshell' known=y url=https://github.com/ksh93/ksh/issues/405
	DO
	(readonly PATH)
	DONE
	TEST title='unset PATH in subshell' known=y url=https://github.com/ksh93/ksh/issues/405
	DO
	(unset PATH)
	DONE

I don't know if these are all different leaks, all the same leak, or neither.

Relevant results on macOS when running DEBUG=y bin/shtests -p leaks:

	leaks.sh[368]: FAIL: known leak: unset PATH in main shell: leaked approx 6596 KiB after 16384 iterations -- help us fix it at: https://github.com/ksh93/ksh/issues/405
	leaks.sh[379]: FAIL: known leak: set PATH value in subshell: leaked approx 9140 KiB after 16384 iterations -- help us fix it at: https://github.com/ksh93/ksh/issues/405
	leaks.sh[384]: FAIL: known leak: run command with preceding PATH assignment in subshell: leaked approx 748 KiB after 16384 iterations -- help us fix it at: https://github.com/ksh93/ksh/issues/405
	leaks.sh[389]: FAIL: known leak: set PATH attribute in subshell: leaked approx 9596 KiB after 16384 iterations -- help us fix it at: https://github.com/ksh93/ksh/issues/405
	leaks.sh[394]: FAIL: known leak: unset PATH in subshell: leaked approx 15964 KiB after 16384 iterations -- help us fix it at: https://github.com/ksh93/ksh/issues/405