bug 873622 - speed up nsXPConnect::GetXPConnect() and rename it since it never returns null r=bholley
bug 873622 - remove some useless xpconnect getters r=bholley
bug 873622 - remove nsIXPConnectWrappedNative::GetXPConnect() r=bholley
bug 873622 - remove XPCCallContext::GetXPConnect() r=bholley
bug 876515 - make the default constructor for TimeStamp{,Value} constexpr r=froydnj

 I had to remove the assert in the windows TimeStampValue::TimeStampValue() so
it could be constexpr.  another option would be to make the constructors being
constexpr conditional on DEBUG, but that requires a couple ifdefs, and it just
seems simpler to make that constructor private and assume TimeStamp code itself
won't be so dumb as to pass that constructor a meaningful value expecting
something to be done with it.