-Don't include unistd.h unconditionally as it's not available in Visual
Studio, but include io.h where necessary.
-Avoid C99isms, and use _chsize_s in place of ftruncate when unistd.h is
not available (as in the case of Visual Studio)
This way we don't have to reopen all the time for pure updates,
and we can immediately unlink the shm file to avoid "leaking" them
on improper shutdown.
We don't want to update the window size on configure event, only
the position, as the size is client side controlled. We were
updating to an old size during resizes which causes us to send
surfaces of the wrong size to the daemon.
With this we always roundtrip position change to the webbrowser.
This avoids conflicts when things change from both directions (app and user).
Also, we fake configure evens when there is no web client to ensure
apps get the events.
This (shouldn't) change any behaviour, but it moves the
webserver parts to a separate file, making the broadway display file
smaller and preparing for later separating out the server to its own
process.
