[gtk] (10 commits) Non-fast-forward update to branch wip/otte/for-master

[Benjamin Otte <otte src gnome org>]

The branch 'wip/otte/for-master' was changed in a way that was not a fast-forward update.
NOTE: This may cause problems for people pulling from the branch. For more information,
please see:

 https://wiki.gnome.org/Git/Help/NonFastForward

Commits removed from the branch:

  c9ff95e... build: Add more useful warning flags
  3b020ae... tests: Add a test for changing the hovered widget

Commits added to the branch:

  18b011a... tests: Add a test for changing the hovered widget
  38dcc8f... mountoperation-x11: Fix copy/paste thinko
  dbf051a... rbtree: Simplify code
  423a973... rbtree: Simplify macros
  c7dd598... device: Handle missing axis
  6dd8d2c... icontheme: Don't crash on icon lookup failure
  aed963d... notebook: Don't crash on drags not coming from a notebook
  3449583... treerbtree: Use for loops
  7d45ce8... build: Add more useful warning flags
  deea727... build: Add -Wnull-dereference