science/mcstas-comps: Update to 2.5 and unbreak

While I'm here:

• Add post-install target to strip binary files and create symbolic links to ${PREFIX}/bin (derived from related port science/mcstas to keep in sync)
• Add shebang fix for sasview_generator.py

Changelog that lists the changes since 2.2a:

http://www.mcstas.org/download/CHANGES_McStas

PR: 234590
Submitted by: Erik B. Knudsen (maintainer)
Reviewed by: tcberner (mentor)
Approved by: miwi (mentor)
Differential Revision: https://reviews.freebsd.org/D19228