Fix lost chunks during streaming of large volumes of data.

[jmptbl]

The current streaming implementation allows for chunks of data to be lost in VSSH's default select{} cases, if volumes of data arrive at a rate too high to be processed. The default cases get selected when the write channel buffer becomes full and would block. This patch puts a client into a streaming mode when the GetStream() function is called, which causes a blocking select{} to be used until the streaming mode is ended.

I confirm that this contribution is made under the terms of the license found in the root directory of this repository's source tree and that I have the authority necessary to make this contribution on behalf of its copyright owner.