opentxs: fix -Wuseless-cast
Merge pull request #316 from toxeus/fixUselessCast

opentxs: fix -Wuseless-cast
fix return types
use error codes instead of OT_FAIL
Merge pull request #318 from mhamrle/otapi_checks_2

Otapi checks 2
Cleanup includes.
MainFile: don't use OTString for version string.
Merge pull request #320 from benma/includes

OTString: forward declare / eliminate
split method processXmlNode
OTMessage: move code to updateContentsByType