- Update to `graphics/appleseed' to version 1.7.1-beta
- OSL support is no longer optional. It complicated the code and the build system, and developers' intention is to make OSL a first-class citizen in appleseed; keeping OSL optional did not allow moving in that direction
- Add a work-around for Core Working Group (CWG) Defect 253: prior to GCC 4.6.4 and Clang 3.9.0, C++ required a user-provided default ctor to default-construct a const object [*], and we still have supported FreeBSD versions where Clang behaves the old way
Because GitHub releases (tarballs) are not fetched with correct modification
time, set TIMESTAMP to 1501170801 which corresponds to commit ae7f346 tagged
as this release.