Don't make the gl flags API

We need to export the symbols so they can be used in the
inspector, but we don't really want to make this supported
public API, so keep them out of installed headers.
inspector: include private gdk headers

...the advantages of living in the same tree.
Revert "Add new API to docs"

This reverts commit 41e9eaf64fdabf49679db193778b15c44e3d0b52.
treeview: remove single-click activation from GtkGestureMultiPress::pressed

This is already handled in GtkGestureMultiPress::release, and more in
concordance with how it was done pre-gestures.

https://bugzilla.gnome.org/show_bug.cgi?id=737891
gtkwindow: claim the press sequence when clicking on the titlebar

This event might not have an action yet, but certainly accounts, and
should be triggering recognition.

This fixes a crash when attempting to drag CSD windows through touch. As
since cfaec2d2f542, gtk_gesture_single_get_current_sequence() would
rightfully return NULL if the gesture didn't enter recognition, making
event lookup fail.