Previously, we'd use a lossy conversion that would replace
funky sequences with the unicode replacement character.
This commit will instead print the bad bytes as hex-escaped characters.
This can be useful when troubleshooting things in tests; this commit
also turns up info logging for the lua test runner so that we can see
that, although nothing else in this commit actually calls that.
I did use it while troubleshooting things just now though, so it is
generally useful.
This allows a (more or less) arbitrary lua function to be used to load
data.
The primary advantage of this is that the size of the resulting
KeySource struct is smaller than it would be to hold the actual data
inline. It also enables the surrounding code to be slightly better
factored.
Wez Furlong