signals: No need to use atomics for Handler refcount
signals: No need to use atomics for Handler refcount

handler_ref and handler_unref_R are always called with the signal
lock held. This is obvious for handler_unref_R as it even sometimes
drops this lock, and can be verified quickly for handler_ref by looking
at all call sites.

This improves the performace about 6% on the emit-handled and the
emit-handled-generic tests.

https://bugzilla.gnome.org/show_bug.cgi?id=694253

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