shim 15

• better checking for bad linker output
• flicker-free console if there's no error output
• improved http boot support
• better protocol re-installation
• dhcp proxy support
• tpm measurement even when verification is disabled
• REQUIRE_TPM build flag
• more reproducable builds
• measurement of everything verified through shim_verify()
• coverity and scan-build checker make targets
• misc cleanups
• currently we don't support multiple certificates in our local
  certificate databases, but pjones was wrong about why, and it's not
  Michael Brown's fault at all. Please disregard the statement in
  commit cdbfb5a