Ensure outside selection pastes are respected

We were resetting the selection on every auxclick, meaning outside
selections could not be pasted in when the terminal had a current
selection.

src/SelectionManager.ts

@@ -293,8 +293,10 @@ export class SelectionManager extends EventEmitter {
 
   /**
    * Queues a refresh, redrawing the selection on the next opportunity.
+   * @param isNewSelection Whether the selection should be registered as a new
+   * selection on Linux.
    */
-  public refresh(fromMouseEvent?: boolean): void {
+  public refresh(isNewSelection?: boolean): void {
     // Queue the refresh for the renderer
     if (!this._refreshAnimationFrame) {
       this._refreshAnimationFrame = window.requestAnimationFrame(() => this._refresh());
@@ -302,7 +304,7 @@ export class SelectionManager extends EventEmitter {
 
     // If the platform is Linux and the refresh call comes from a mouse event,
     // we need to update the selection for middle click to paste selection.
-    if (Browser.isLinux && fromMouseEvent) {
+    if (Browser.isLinux && isNewSelection) {
       const selectionText = this.selectionText;
       if (selectionText.length) {
         this.emit('newselection', this.selectionText);