Vala 0.51.3
===========
 * Various improvements and bug fixes:
  - codegen:
    + Don't use volatile modifier in glib API when targetting >= 2.68 [glib!1719]
    + CCodeBaseModule.get_type_id_expression () won't return null
    + Don't wrongly emit declaration for default-handler of signals
    + Include "string.h" for strcmp() (POSIX)
  - vala:
    + Generics value holding struct pointer requires casting on access [#347]
    + Infer needle type for "in" expression on enum [#1138]
    + Don't allow "in" operation with different enum types [#1139]
    + Improve context check whether property is writeable on assignments
    + Include "stdlib.h" for Enum.to_string() (POSIX) [#1143]
    + Set proper source_reference for implicit "this" and "result" variables
    + Report error for invalid inner operand of unary expressions
  - girwriter: Output default handler of signals

 * Bindings:
  - glib-2.0: Add new symbols from 2.68
  - webkit2gtk-4.0: Update to 2.31.90
  - vapi: Update GIR-based bindings