Enforce HTTP 1.0 in estclient

estclient does not properly handle respones from an EST server with

Transfer-Encoding: chunked

which happens to be a standard HTTP 1.1 feature. To force EST servers to reply w/o chunked encoding, send HTTP 1.0 requests rather than 1.1.

In particular, this fixes an incompatiblity with the globalsign/est [1] test implementation.

[1] https://github.com/globalsign/est