opentxs-crypto: fix -Wredundant-decls
Fix command showaccounts

OTAPI_Wrap::GetAccountWallet_Name is used to get account wallet name. The name could be empty so name emptiness should not be used for testing account existence.

Closes #256
Merge pull request #271 from toxeus/fixRedundantDecls

opentxs-crypto: fix -Wredundant-decls
Merge pull request #275 from mhamrle/issue_256_showaccounts

Fix command showaccounts
OTString: move fwrite_string() into caller

It doesn't make sense to have a separate function which is
used only in one place.
Merge pull request #278 from toxeus/removeFwriteString

OTString: move fwrite_string() into caller