gtk+-3.0: Update to 3.13.6~
Add some missing get_used_variables methods

Fixes bug 734315
Add Simon Werbeck to THANKS
Report an error when parsing non-public struct fields

Fixes bug 683413
webkit2gtk: Update to 2.5.2
glib: make the parameter of VariantDict constructor nullable

The underlying glib implementation accepts null to initialize an empty
dictionary. The vapi now reflects this, defaulting the single parameter
to null.

Fixes bug 734612
glib-2.0: make VariantDict.end return a floating reference

The underlying implementation returns a floating reference. Reflecting
this in the vapi silences the warning about g_variant_unref called once
too many.

Fixes bug 734611
linux: improve backtrace bindings

Some minor improvements have been made to backtrace_symbols; we no
longer leak the return value and it is marked as nullable. This also
adds a Backtrace namespace for some better bindings which treat the
backtrace as an array of void* instead of just a void*.
parser: Report error only for private instance fields in structs

Fixes bug 734787