make.go: block darwin/386 builds by default

Fixes Issue 155

Change-Id: I91d471c7557c2225f5feb6b33cc6bb7cc381a68f
httputil: don't set Content-Type until we're sure

Fixes Issue 182

Change-Id: I1a687c51b60caca5ddc7b4cd21d4f7efa6342248
httputil: rename conn to rw, per current conventions

Change-Id: Ifc39915396f5ababdc2fb21c2a95156bbbf729c8
blobpacked: start of untested blob streaming code

Will be used for recovery.

Change-Id: I8a6d219086a306e53b1b621b7bc7cf59b984c765
C+A: add Matthieu Rakotojaona (Individual CLA)

Change-Id: Ic24976e558c6e3d2ca0f7ebc987d09f1639af57c