[btcsuite/btcwallet] 2181f4: votingpool: implement Pool.StartWithdrawal()

[Guilherme Salgado]

  Branch: refs/heads/master
  Home:   https://github.com/btcsuite/btcwallet
  Commit: 2181f4859dc8040347b2ed3a2449d139585ca461
      
https://github.com/btcsuite/btcwallet/commit/2181f4859dc8040347b2ed3a2449d139585ca461
  Author: Guilherme Salgado <gsalg...@gmail.com>
  Date:   2015-04-01 (Wed, 01 Apr 2015)

  Changed paths:
    M txstore/tx.go
    A votingpool/common_test.go
    M votingpool/db.go
    A votingpool/db_wb_test.go
    M votingpool/doc.go
    A votingpool/error.go
    A votingpool/error_test.go
    M votingpool/example_test.go
    A votingpool/factory_test.go
    A votingpool/input_selection.go
    A votingpool/input_selection_wb_test.go
    M votingpool/internal_test.go
    A votingpool/log.go
    M votingpool/pool.go
    M votingpool/pool_test.go
    A votingpool/pool_wb_test.go
    M votingpool/test_coverage.txt
    A votingpool/test_data_test.go
    A votingpool/withdrawal.go
    A votingpool/withdrawal_test.go
    A votingpool/withdrawal_wb_test.go
    M waddrmgr/error.go
    M waddrmgr/error_test.go
    R waddrmgr/pool_error.go

  Log Message:
  -----------
  votingpool: implement Pool.StartWithdrawal()

<http://opentransactions.org/wiki/index.php/Voting_Pool_Withdrawal_Process>

Also includes some refactorings and other improvements, including better docs
and a new error type (votingpool.Error) used for all votingpool-specific
errors.