Golang http server strips off 'Expect' header, if the
client sent this as part of signed headers we need to
handle otherwise we would see a signature mismatch.
`aws-cli` sets this as part of signed headers which is
a bad idea since servers trying to implement AWS
Signature version '4' will all encounter this issue.
According to
http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.20
Expect header is always of form:
Expect = "Expect" ":" 1#expectation
expectation = "100-continue" | expectation-extension
So it safe to assume that '100-continue' is what would
be sent, for the time being keep this work around.
This convenience was necessary to be used for golang library functions like io.Copy and io.Pipe
where we shouldn't be writing proxies and alternatives returning *probe.Error
This change also brings more changes across code base for clear separation regarding where an error
interface should be passed encapsulating *probe.Error and where it should be used as is.
Harshavardhana