Do not hardcode stunnel directory path, just make sure that is installed
in user '$PATH'. it is required for 'mailfs -t' TLS support, so printout
an error string if it was not found.
Tested with latest stunnel version 5.17 on OpenBSD and macosx.
% mailfs -t imap.gmail.com ; echo $?
0
Change-Id: Icbd507c7efa81ef2aa7aed37bec5f639b37526cb
Reviewed-on: https://plan9port-review.googlesource.com/1280
Reviewed-by: Russ Cox <rsc@swtch.com>
71de840f05