Add wallet2::verify_password method

Allows wallet password to be verified without changing wallet state.
Add simple_wallet::seed_set_language method

Add simple_wallet::set_variable method to provide top-level "set"
command and support "set seed language" command.
wallet2::load correctly initialize m_blockchain for wallet loaded without bin file

Fix for simplewallet loading a wallet with a keys file but no bin file.

  - this situation previously required a user to restart simplewallet
    before it would refresh its blockchain from the server.
wallet2::rewrite update to not require bin file

Allow pre-JSON wallet format to load without depending on existing bin
file.

Don't write bin file while inside keys rewrite, so bin file write
behavior here matches that of regular wallet load.
Repeat prompt for wallet path if invalid

simplewallet run without a wallet path argument should prompt again if
an invalid path was entered.

Validity here currently means the string isn't empty.
Document existing function
Merge pull request #205

b261448 revert the removal of the 'arch' flag from the release-static target (Riccardo Spagni)
a956f07 added gpg key for warptangent (Riccardo Spagni)
ac19084 revert the removal of the 'arch' flag from the release-static target (Riccardo Spagni)
Merge pull request #200

cfc8c55 Add simple_wallet::seed_set_language method (warptangent)
26b87df Add wallet2::verify_password method (warptangent)
Merge pull request #201

9b7e0a0 wallet2::load correctly initialize m_blockchain for wallet loaded without bin file (warptangent)
Merge pull request #202

d7aafd5 wallet2::rewrite update to not require bin file (warptangent)
Merge pull request #203

583cf0a Document existing function (warptangent)
95eb944 Repeat prompt for wallet path if invalid (warptangent)