configure.ac: Use maintainer mode by default
configure.ac: Use maintainer mode by default

See
https://mail.gnome.org/archives/desktop-devel-list/2011-September/msg00064.html

GNOME/gsettings-desktop-schemas,Distrotech/gsettings-desktop-schemas,GNOME/gsettings-desktop-schemas,Distrotech/gsettings-desktop-schemas