games/iortcw: Update to 1.5a

• Update iortcw to 1.5a
• Use DISTVERSION instead of PORTVERSION
• Bump PORTEPOCH
• Disable use of OpenAL to fix segmentation faults on FreeBSD 11.0-RELEASE
• Dynamically adjust pkg-message

PR: 214959
Submitted by: Tobias Kortkamp <t@tobik.me> (maintainer)
Reviewed by: junovitch
Approved by: junovitch (mentor)