Allowing developers to optionally disable MD5 content validation.

[RachBreeze]

Hello

I have raised this PR because we are seeing the error at below on a client site.

This impacts a large number of files. The files:

• open without issue directly from blob storage
• are not large

Kind regards

Rachel

[StorageException: Calculated MD5 does not match existing property]
   Microsoft.WindowsAzure.Storage.Core.Executor.Executor.ExecuteSync(RESTCommand`1 cmd, IRetryPolicy policy, OperationContext operationContext) in c:\Program Files (x86)\Jenkins\workspace\release_dotnet_master\Lib\ClassLibraryCommon\Core\Executor\Executor.cs:604
   Microsoft.WindowsAzure.Storage.Blob.CloudBlob.DownloadToStream(Stream target, AccessCondition accessCondition, BlobRequestOptions options, OperationContext operationContext) in c:\Program Files (x86)\Jenkins\workspace\release_dotnet_master\Lib\ClassLibraryCommon\Blob\CloudBlob.cs:235
   Our.Umbraco.FileSystemProviders.Azure.AzureFileSystem.OpenFile(String path) +226
   Our.Umbraco.FileSystemProviders.Azure.FileSystemVirtualFile.Open() +475
   System.Web.HttpResponse.WriteVirtualFile(VirtualFile vf) +33
   System.Web.StaticFileHandler.ProcessRequestForNonMapPathBasedVirtualFile(HttpRequest request, HttpResponse response, String overrideVirtualPath) +168
   System.Web.StaticFileHandler.ProcessRequestInternal(HttpContext context, String overrideVirtualPath) +90
   System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +872
   System.Web.<>c__DisplayClass285_0.<ExecuteStepImpl>b__0() +40
   System.Web.HttpApplication.ExecuteStepImpl(IExecutionStep step) +155
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +94

[Jeavon]

@RachBreeze I think perhaps you have targetted the wrong base branch?