Fix regression in http.c for long-polling connections; add lazy initialization of database connections, to avoid the overhead in handlers that don't use SQL

type r1 = {A : string, B : string}
type r2 = {B : string, A : string}

val show_r1 : show r1 = mkShow (fn r => r.A ^ "+" ^ r.B)
val show_r2 : show r2 = _