GOutputStream: Split _close_async for internal use
GOutputStream: Split _close_async for internal use

Refactor g_output_stream_close_async() into itself and an internal
variant for potential use inside other operations (splice_async).
The internal version must be called between
g_output_stream_set_pending() and g_output_stream_clear_pending().

https://bugzilla.gnome.org/show_bug.cgi?id=691581

cention-sany/glib,mzabaluev/glib,tamaskenez/glib,cention-sany/glib,cention-sany/glib,cention-sany/glib,krichter722/glib,tchakabam/glib,lukasz-skalski/glib,Distrotech/glib,endlessm/glib,krichter722/glib,mzabaluev/glib,gale320/glib,mzabaluev/glib,lukasz-skalski/glib,tchakabam/glib,MathieuDuponchelle/glib,johne53/MB3Glib,tamaskenez/glib,johne53/MB3Glib,cention-sany/glib,endlessm/glib,lukasz-skalski/glib,MathieuDuponchelle/glib,gale320/glib,tamaskenez/glib,tamaskenez/glib,endlessm/glib,MathieuDuponchelle/glib,krichter722/glib,tchakabam/glib,johne53/MB3Glib,ieei/glib,endlessm/glib,MathieuDuponchelle/glib,Distrotech/glib,mzabaluev/glib,gale320/glib,mzabaluev/glib,tchakabam/glib,endlessm/glib,ieei/glib,lukasz-skalski/glib,gale320/glib,MathieuDuponchelle/glib,Distrotech/glib,johne53/MB3Glib,johne53/MB3Glib,tchakabam/glib,johne53/MB3Glib,gale320/glib,krichter722/glib,tamaskenez/glib,krichter722/glib,ieei/glib,ieei/glib,Distrotech/glib,ieei/glib,lukasz-skalski/glib,Distrotech/glib