Simpler reimplementation of SS's patch; just plumb file and line through
inline functions in header.  We add a new check, which actually tests
these, and fix _info which missed ccan/check_type as a dependency.
Based-on-the-true-story-by: Stewart Smith <stewart@linux.vnet.ibm.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>