libraw: style nit
libraw: fix deps

Jasper is picked up as an undeclared dependency if present, so add it.
lcms2 isn't found without pkg-config, so add it.
libraw: build packs out of separate folders

Downloading the two paths to the build root works, but clobbers libraw's
own meta files.

Build the packs out of separate folders to keep original meta files.
figlet: style nits
Remove keg test dependency on formula
Remove hardcoded paths in keg tests
Add tests to demonstrate failure to prune empty directories
Keep track of pruned parent directories
Always prune empty toplevel directories when unlinking