editors/emacs: Update to version 25.2

[jrm]

Summary

• Make gtk3 the default X11 toolkit since gtk3 is upstream's first choice and upstream considers gtk2 deprecated.

• Upstream release notes: https://www.gnu.org/software/emacs/news/NEWS.25.2

Test Plan

portlint -C: warning about adding an NLS knob
testport: OK (poudriere: 10.3-RELEASE-p10, i386, default options)
testport: OK (poudriere: 10.3-RELEASE-p10, amd64, default options)
testport: OK (poudriere: 11.0-RELEASE-p1, i386, default options)
testport: OK (poudriere: 11.0-RELEASE-p1, amd64, default options)

All other options except xwidgets were tested. A poudriere testport run
with xwdigets turned on is running now, but will take about 8 hours for
webkit-gtk3 to compile. I will report back when it completes.

[jrm]

The build also succeeded (under 11amd64) with xwidgets turned on.

[ashish]

Works fine for me too. Please go ahead and commit.

Thank you

[jrm]

Committed in r439187 (I forgot to reference the revision in the commit message).