Add Swift-specific MD5 checksum header

Tested against cloudfiles-us, hpcloud-objectstorage, and
swift-keystone.  Reference for ETag:

https://answers.launchpad.net/swift/+question/157064
JCLOUDS-161: large blob support for Azure

Large blob support for AzureClient; the next step of this is to
support PutOptions.multipart and digest a blob into 4M parts. This
just implements the Azure interaction.
Set provider id in AtmosClientLiveTest

This allows Atmos live tests to run.
[trivial] demote Boolean to primitive
Add Atmos-specific MD5 checksum header

Tested that Atmos Online and Synaptic Atmos both enforce this.
Upgrade to gson 2.2.4
https://issues.apache.org/jira/browse/JCLOUDS-117
Introduce StripExpectHeader filter and a property to control it.

Some providers (specifically HP Cloud and Google Cloud Storage) do not
properly support Expect: 100-continue headers. JDK7 is stricter in its
handling of the Expect header than JDK6 -- in particular, it expects
servers to properly respond to an expect header and times out only if a
prior timeout did not exist on the underlying HTTP connection. As a
result, JDK7 tests against these providers hang and fail.

This commit introduces a new filter -- appropriate called
StripExpectHeader -- that is controlled by the property
jclouds.strip-expect-header. The property defaults to false to preserve
existing behavior but allows applications to tweak Expect header
handling.

Tested by running HPCS live tests with JDK7 -- previously most of these
tests would fail with timeouts.

Closes JCLOUDS-181
Do not eagerly check for existence in FilePayload

This is a TOCTOU violation and FilePayload.getInput already propagates
this.  This commit allows external callers like jclouds-cli to
introspect on the exception type, returning a more friendly error
message in some situations.
Expect exception from FilePayload.getInput

Previously the constructor threw this.  Fixes regression from ac58a70.
Cleanup of Azureblob code; as per pull request review. Additional items
not covered here are assigned specific bug ids.
Revert "Add Atmos-specific MD5 checksum header"

This reverts commit 98230e60a4e47c94ffe65f50470cf5ad51ca3f67.

This succeeded in my tests but integration tests fail.
Follow-up to Azureblob cleanup

See discussion at https://github.com/jclouds/jclouds/pull/66
Allow skipping duplicate-finder-plugin by setting skipDuplicateFinder property to true