Added wxFileName::Exists().

This function checks for existence of anything with the given name, not
necessarily just a file or a directory.

Extend the unit test to verify that it returns true for /dev/null on Unix
systems.

Closes #953.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@70600 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/filename.cpp

@@ -732,6 +732,12 @@ bool wxFileName::DirExists( const wxString &dirPath )
     return wxFileSystemObjectExists(dirPath, wxFileSystemObject_Dir);
 }
 
+/* static */
+bool wxFileName::Exists(const wxString& path)
+{
+    return wxFileSystemObjectExists(path, wxFileSystemObject_Any);
+}
+
 // ----------------------------------------------------------------------------
 // CWD and HOME stuff
 // ----------------------------------------------------------------------------