Clear import error state on logout.

ui/app/accounts/import/private-key.js

@@ -17,6 +17,10 @@ function PrivateKeyImportView () {
   Component.call(this)
 }
 
+PrivateKeyImportView.prototype.componentWillUnmount = function () {
+  this.props.dispatch(actions.displayWarning(null))
+}
+
 PrivateKeyImportView.prototype.render = function () {
   const { error } = this.props
 

ui/app/components/account-menu/index.js

@@ -32,6 +32,7 @@ function mapDispatchToProps (dispatch) {
     },
     lockMetamask: () => {
       dispatch(actions.lockMetamask())
+      dispatch(actions.displayWarning(null))
       dispatch(actions.toggleAccountMenu())
     },
     showConfigPage: () => {