[MERGE] Make bzrlib.smart.medium use lazy imports

[Andrew Bennetts]

John Arbash Meinel wrote:
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> This is my hack-around for the problems with Crypto.Util.randpool
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> Basically, my making the imports in bzrlib.smart.medium be lazy, just
> running the test suite doesn't have to import transport.ssh, which means
> it doesn't have to create a RandomPool object.

bb:approve

-Andrew.