Update clippy version and address new warnings

Cargo.toml

@@ -23,7 +23,7 @@ trace = []
 time = "~0.1.0"
 bitflags = "~0.1"
 libc = "~0.2"
-clippy = {version = "~0.0.41", optional = true}
+clippy = {version = "~0.0.58", optional = true}
 
 [dev-dependencies]
 tempdir = "~0.3.4"

src/error.rs

@@ -143,18 +143,19 @@ impl error::Error for Error {
     fn cause(&self) -> Option<&error::Error> {
         match *self {
             Error::SqliteFailure(ref err, _) => Some(err),
-            Error::SqliteSingleThreadedMode => None,
             Error::FromSqlConversionFailure(ref err) => Some(&**err),
             Error::Utf8Error(ref err) => Some(err),
             Error::NulError(ref err) => Some(err),
-            Error::InvalidParameterName(_) => None,
+
+            Error::SqliteSingleThreadedMode |
+            Error::InvalidParameterName(_) |
+            Error::ExecuteReturnedResults |
+            Error::QueryReturnedNoRows |
+            Error::GetFromStaleRow |
+            Error::InvalidColumnIndex(_) |
+            Error::InvalidColumnName(_) |
+            Error::InvalidColumnType |
             Error::InvalidPath(_) => None,
-            Error::ExecuteReturnedResults => None,
-            Error::QueryReturnedNoRows => None,
-            Error::GetFromStaleRow => None,
-            Error::InvalidColumnIndex(_) => None,
-            Error::InvalidColumnName(_) => None,
-            Error::InvalidColumnType => None,
 
             #[cfg(feature = "functions")]
             Error::InvalidFunctionParameterType => None,

src/lib.rs

@@ -53,6 +53,9 @@
 #![cfg_attr(feature="clippy", feature(plugin))]
 #![cfg_attr(feature="clippy", plugin(clippy))]
 
+// Clippy complains about SQLite in our doc comments, but they're fine.
+#![cfg_attr(feature="clippy", allow(doc_markdown))]
+
 extern crate libc;
 extern crate libsqlite3_sys as ffi;
 #[macro_use]
@@ -791,10 +794,10 @@ impl<'conn> Statement<'conn> {
         ffi::sqlite3_reset(self.stmt);
         match r {
             ffi::SQLITE_DONE => {
-                if self.column_count != 0 {
-                    Err(Error::ExecuteReturnedResults)
-                } else {
+                if self.column_count == 0 {
                     Ok(self.conn.changes())
+                } else {
+                    Err(Error::ExecuteReturnedResults)
                 }
             }
             ffi::SQLITE_ROW => Err(Error::ExecuteReturnedResults),