Add prose explaining what each test does, and inline comments where
appropriate.

Add structs and types to facilitate the explicitly declared authority
level described in issue #2.

May or may not be revisiting this to tweak it later... :P

Previously, the fork_database and chainbase undo histories were never
getting trimmed, so they'd grow forever. Fixed.

Also some improvements around how to use chainbase, particularly,
setting the revision after a reindex, and also acquiring locks
appropriately. Note that there's a lot of lock acquiring that still
needs to be added; I didn't realize I needed to do this before :]

As of this commit, we only write irreversible blocks to disk, and when
we reopen the database, we rewind the state until the head block is the
last irreversible block.

The unit tests are doing their jobs: several of them broke due to this
change, because the tests which checked that the head block number
didn't change during a restart of the database were invalidated by this
change: the head block number *should* now change in a restart; it
should revert to the last_irreversible_block_num. The tests are updated
to account for this, and all pass again.

Preparing for only writing irreversible blocks to disk; first I needed to
update the various block fetching methods on database to account for
this. This commit contains those updates, as well as a shiny new unit
test to make sure those methods are still working correctly.

The LIB was already being calculated and stored in the
dynamic_global_property_object, but now I know it was! :D

Also remove a redundant block from node.cpp (the removed block was
functionally equivalent to the FC_LOG macro following it)

I've already removed operations from the system; in this commit I add a
new message type and integrate it into the transaction type.

Also remove transaction_evaluation_state and the size_checker program.

Don't need it anymore!

All the db_*.cpp sources are now merged together in database.cpp again.

Everything related to the maintenance interval is now gone, including
(and especially, really) the skipped blocks during the maintenance
period.

...even though there's a waiting pull request. By bumping it, I make it
break when people try to sync it, so at least it's obvious that it's not
working right now.

Once https://github.com/bytemaster/chainbase/pull/3 is merged, I can
bump it again to fix it.

- Cleaned out some cruft
- Added some new macros to remove boilerplate
- Added some more test cases

Add a testing_network class to emulate a P2P network ferrying blocks
between databases.

Add some test cases exercising databases syncing with the
testing_network and resolving forks.

This test case checks some invariants around the missing of blocks.