Implementing GUID using boost

I haven't taken a look at the hash table stuff, so I didn't touch that, but I was able to get rid of our (respectable!) guid random number seeding stuff in `guid_init`, etc. I ran the test suite and uncovered one problem which I was able to fix. I also started the program with a moderately sized chart and transactions (my mom's business's books), and everything seems good.
I think
```
boost::uuids::uuid repl_guid = gen ();
val->swap (repl_guid);
```
would be cleaner and maybe faster.