A common pattern that we see clients do is send a HEAD request before a
PUT to see if it exists. This can slow things down quite a bit
especially since 404s on HEAD are currently a bit expensive.
This change will allow a client to include a "If-None-Match: *" header
with a PUT request. In combination with "Expect: 100-Continue" this
allows the server to return that it already has a copy of the object
before any data is sent.
I attempted to also include etag support with the If-None-Match header,
but that turned up having too many hairy edge cases, so was left as a
future excercise.
DocImpact
Change-Id: I94e3754923dbe5faba065719c7a9afa9969652dd
0b893825eb