File System view: Add "New Folder" to context menu

Task-number: QTCREATORBUG-17358
Change-Id: I64b3d34ca0432369630382c40cf749f3cc1a08df
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>

src/libs/utils/fileutils.cpp

@@ -726,6 +726,13 @@ bool FileName::operator>=(const FileName &other) const
     return other <= *this;
 }
 
+FileName FileName::operator+(const QString &s) const
+{
+    FileName result(*this);
+    result.appendString(s);
+    return result;
+}
+
 /// \returns whether FileName is a child of \a s
 bool FileName::isChildOf(const FileName &s) const
 {