This introduces CNetAddr and CService, respectively wrapping an
(IPv6) IP address and an IP+port combination. This functionality used
to be part of CAddress, which also contains network flags and
connection attempt information. These extra fields are however not
always necessary.

These classes, along with logic for creating connections and doing
name lookups, are moved to netbase.{h,cpp}, which does not depend on
headers.h.

Furthermore, CNetAddr is mostly IPv6-ready, though IPv6
functionality is not yet enabled for the application itself.

IsStandardInputs could crash if given invalid input index.

This reverts commit 21d9f367.

Code cleanup: use ECDSA_size() instead of fixed 10,000 byte sig buffer, and explicity init static var

so it takes a flag for how to interpret OP_EVAL.
Also increased IsStandard size of scriptSigs to 500 bytes, so
a 3-of-3 multisig transaction IsStandard.

OP_EVAL is a new opcode that evaluates an item on the stack as a script.
It enables a new type of bitcoin address that needs an arbitrarily
complex script to redeem.

During the rushed transition from 0.01 BTC to 0.0005 BTC fees, we took the
approach of dropping the relay and block-inclusion fee to 0.0005 BTC
immediately, and only delayed adjusting the sending fee for the next release.
Afterward, the relay fee was lowered to 0.0001 BTC to avoid having the same
problem in the future. However, the block inclusion code was left setting
fForRelay to true! This fixes that, so the lower 0.0001 BTC allowance is (as
intended) only permitted for real relaying.

Added RPC call 'getmemorypool' that provides everything needed to construct a block with a custom generation transaction and submit a solution

getmemorypool [data]
If [data] is not specified, returns data needed to construct a block to work on:
  "version" : block version
  "previousblockhash" : hash of current highest block
  "transactions" : contents of non-coinbase transactions that should be included in the next block
  "coinbasevalue" : maximum allowable input to coinbase transaction, including the generation award and transaction fees
  "time" : timestamp appropriate for next block
  "bits" : compressed target of next block
If [data] is specified, tries to solve the block and returns true if it was successful.

- fixes problem that one misconfigured or malicious node can mess up progress bar
- implementation in src/util.h
- testcase in src/test/util_tests.cpp

clarify function signature (GetNumBlocksOfPeers) and use number of 'frozen' blocks as initial value for number of peer blocks

Bugfix: Use timestamp in coinbase rather than "bits", needed to ensure coinbase txn is unique even if address is the same

Patch from ArtForz, who discovered the problem.

Renames GetOrReuseKeyFromKeyPool to GetKeyFromPool, with fAllowReuse arg and bool result.

Collapsed multiple wallet mutexes to a single cs_wallet, to avoid deadlocks with wallet methods that acquired locks in different order.
Also change master RPC call handler to acquire cs_main and cs_wallet locks before executing RPC calls; requiring each RPC call to acquire the right set of locks in the right order was too error-prone.