Sync devhelp 3.20.0-2 (main) from Debian unstable (main)

Please sync devhelp 3.20.0-2 (main) from Debian unstable (main)

Explanation of the Ubuntu delta and why it can be dropped:
  * Undo that, use wk2 now.
  * Fix the -dev package dependency too.
  * debian/patches/0001-Revert-Use-webkit_navigation_policy_decision_get_nav.patch,
    debian/control{,.in}: Use webkit2-3.0 since 2-4.0 isn't in main yet.
  * No-change rebuild for python3.5 transition
  * Revert until this is dropped to universe or webkit2gtk is main: LP: #1459434
    - debian/control.in:
      + Switch to libwebkit2gtk-4.0-dev.
      + Break anjuta << 2:3.14.0-2 to prevent anjuta from mixing
        libwebkit2gtk-3.0 and libwebkit2gtk-4.0.

Since Ubuntu main is using WebKit2 now, there is no remaining diff.
This package has been tested for months in the GNOME3 Staging PPA for Xenial.

Changelog entries since current yakkety version 3.18.1-1ubuntu5:

devhelp (3.20.0-2) unstable; urgency=medium

  * Upload to unstable.
  * Update dependencies of libdevhelp-dev to match the versions in
    Build-Depends.
  * Bump Standards-Version to 3.9.8.

 -- Michael Biebl <email address hidden> Sun, 17 Apr 2016 18:00:44 +0200

devhelp (3.20.0-1) experimental; urgency=medium

  * Bump gtk+ build-dependency to >= 3.16 (Closes: #808995)
  * New upstream release.
  * Update build-dependencies according to configure.ac changes:
    - Bump gtk+ to >= 3.19.3

 -- Andreas Henriksson <email address hidden> Sun, 03 Apr 2016 13:02:40 +0200