GOptionContext: Improve help in simple cases
GOptionContext: Improve help in simple cases

Only add [OPTION...] to the usage line if the context
has options. And shorten "Application Options" to just
"Options" if we don't have to differentiate from other
kinds of options.

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