* actix-multipart: Fix multipart boundary reading
If we're not ready to read the first line after the multipart field
(which should be a "\r\n" line) then return Pending instead of Ready(None)
so that we will get called again to read that line.
Without this I was getting MultipartError::Boundary from read_boundary()
because it got the "\r\n" line instead of the boundary.
Also tweaks the test_stream test to test partial reads.
This is a forward port of #1189 from 1.0
* actix-multipart: Update changes for boundary fix
* Replace UnsafeCell in DateServiceInner with Cell
The previous API was extremely dangerous - calling `get_ref()`
followed by `reset()` would trigger instant UB, without requiring
any `unsafe` blocks in the caller.
By making DateInner `Copy`, we can use a normal `Cell` instead
of an `UnsafeCell`. This makes it impossible to cause UB (or even panic)
with the API.
* Split unsafe block HttpServiceHandlerResponse
Also add explanation of the safety of the usage of `unsafe`
* Replace UnsafeCell with RefCell in PayloadRef
This ensures that a mistake in the usage of 'get_mut' will cause
a panic, not undefined behavior.
