Checkpoint conversion to new sandbox object/class API.
Build static and produce a dump to ease debugging.
Checkpoint modernization of libimagebox.
Garbage collect some #if 0's code.
Fix a merge error that prevents building.
Add a cheri version of libvuln_png.
Link against the cheri version of vuln_png and directly build the required
libz bits for now.
Modernize sandbox use a bit.

Don't use explicit system object.  Don't pass stack pointers into
libpng, it tries to store them in malloc'd structs.
Don't make the public structures use capabilities, that breaks the
ability to use libimagebox from a capability-oblivious compiler.
Tidy whitespace.
Remove some unneeded headers.
Modernize and fix png rendering in libimagebox.