Fixes #3978: Move r29920 to v1.7 branch (correctly handle the convertor internal stack for persistent receives.)

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r29920 [[BR]]
Don't reset the convertor to the default size and buffer as it 
should be already set to the right value. This fixes a problem
identified by Guillaume Gouaillardet, where using a single 
persistent receive leads to leaking the convertor stack memory.

Refs #3956
cmr=v1.7.4:reviewer=jsquyres:subject=Correctly handle the convertor internal stack for persistent receives.
Fixes #3951: Move GPU Direct RDMA support to 1.7

Add missing updates