Refactor triedb constructors to error on invalid state root (#1230)

* add TrieError, refactor Trie DB creation

* remove Result type alias due to glob import conflicts

* fix fallout in state.rs

* add debug, display impl for TrieError

* fix fallout in account.rs

* ethcore::Error::TrieError variant

* fix remaining fallout in ethcore crate

* added From<TrieError> impl for Error, removed map_err calls

* fix test breakages

* fix doc tests

* update docs

[ci skip]

ethcore/src/error.rs

@@ -224,6 +224,8 @@ pub enum Error {
 	PowHashInvalid,
 	/// The value of the nonce or mishash is invalid.
 	PowInvalid,
+	/// Error concerning TrieDBs
+	TrieError(TrieError),
 }
 
 impl fmt::Display for Error {
@@ -239,6 +241,7 @@ impl fmt::Display for Error {
 				f.write_fmt(format_args!("Unknown engine name ({})", name)),
 			Error::PowHashInvalid => f.write_str("Invalid or out of date PoW hash."),
 			Error::PowInvalid => f.write_str("Invalid nonce or mishash"),
+			Error::TrieError(ref err) => f.write_fmt(format_args!("{}", err)),
 		}
 	}
 }
@@ -300,6 +303,12 @@ impl From<IoError> for Error {
 	}
 }
 
+impl From<TrieError> for Error {
+	fn from(err: TrieError) -> Error {
+		Error::TrieError(err)
+	}
+}
+
 // TODO: uncomment below once https://github.com/rust-lang/rust/issues/27336 sorted.
 /*#![feature(concat_idents)]
 macro_rules! assimilate {