packable -- test packable with cramjet

[Fred T. Hamster]

1. cramjet tester for unpacking:
   1. we should test all unpacking methods with a "cramjet".
   2. this would be a function that would slam the unpack method with tons of bogus data.
   3. to be really effective, it needs to randomize whether the contents are crap or not. the first few fields should be valid a lot of the time in order to test how the last few fields are handled in the presence of crap.
   4. AHA!!! create random object of the specified type. pack them into a byte array. zorch out with garbage various parts of the byte array.
   5. to be really sneaky, zorch the contents with data in a similar range, like ascii for ascii, packed bytes for packed bytes, if this can be determined. maybe not, but it would be cool to replace things with items kind of close but not exactly equal during a portion of the testing.
   6. then unpack the resulting garbage. see how the unpacker behaves. most likely a nasty crash is going to be the result for a bad error; make sure things are bundled in exception handlers as much as possible.