Refer to the json-c library as per their examples.

Not using -I makes more sense to me, but it appears that some distributions
put the headers in different locations, and all the example code refers only
to json.h, so we'll follow suit...

Also link against the correct library.
Use built-in linking rules (with its own variables).
Merge branches 'build-implicit-link' and 'build-jsonc' into integrate

Conflicts:
	cpp/Makefile
WIP on DNS.
Start of test harness.
Return leaf hash.
Temporarily include Eran's https://codereview.appspot.com/66940043/.
Also verify an inclusion proof for a leaf's hash.
Test work in progress.
Get rid of trailing whitespace.
Add missing file, move unmoved file.
Allow binary SCTs and logs on protocols other than HTTPS.
Remaining issues after a rebase.
Fix a couple of stray "https:"s.
Log responses.
Correct path.
Show error content.
Identify the type of the cert in the file name.
Calculate the right audit path length.
Get rid of cruft.