Merge branch 'jk/harden-protocol-v2-delim-handling'

The server-end of the v2 protocol to serve "git clone" and "git
fetch" was not prepared to see a delim packets at unexpected
places, which led to a crash.

* jk/harden-protocol-v2-delim-handling:
  test-lib-functions: simplify packetize() stdin code
  upload-pack: handle unexpected delim packets
  test-lib-functions: make packetize() more efficient