2.57.1: (unstable):
Distro packagers should probably not package this yet.

Gio:
* DataOutputStream::put_string(): Don't pass std:string by value
  (Kjell Ahlstedt)

gmmproc:
* Add _MEMBER_SET_STR() macro
  (Pavlo Solntsev) Bug #793778

Build:
* Change the ABI to glibmm-2.58
  (Kjell Ahlstedt)