darktable: Update to 1.6.0

[dumbbell]

Summary

Beside the update:

• OSVERSION + USE_GCC are replaced by USES=compiler:c++11-lib
• new option: LIBSECRET (required GNOME 3)
• options turned on by default: SLIDESHOW, SQUISH

[antoine]

graphics/darktable/Makefile

100–101

I think you can change it back to bsd.port.options.mk/bsd.port.mk
Is there a special reason to use bsd.port.pre.mk/bsd.port.post.mk?

[dumbbell]

Replace bsd.port.{pre,post}.mk by bsd.port.options.mk/bsd.port.mk

[dumbbell]

In D1311#4, @antoine wrote:

I think you can change it back to bsd.port.options.mk/bsd.port.mk
Is there a special reason to use bsd.port.pre.mk/bsd.port.post.mk?

I don't remember why, so I switched back to bsd.port.options.mk/bsd.port.mk.

[antoine]

LGTM

[dumbbell]

Committed as rP374758.