Allow for late binding in DrupalPublicStreamWrapper's getExternalUrl() method

Problem/Motivation

The Public Stream Wrapper uses self::getDirectoryPath() to call the getDirectoryPath() method in an instantiated object context. This means that PHP does early binding and calls DrupalPublicStreamWrapper's getDirectoryPath() method, even when using a stream wrapper that inherits from DrupalPublicStreamWrapper. This means that you have to redefine getExternalUrl() in your custom stream wrapper class just to use your overridden getDirectoryPath() method.

Proposed resolution

Make getExternalUrl() call the current instance's getDirectoryPath() method instead of DrupalPublicStreamWrapper's version of that method.

Remaining tasks

Re-roll patch.

User interface changes

None.

API changes

PublicStream will work slightly differently (in a good way).

Original report

For some reason, the public stream wrapper uses self::getDirectoryPath() to call the getDirectoryPath() method in an instantiated object context. This means that PHP does early binding and calls DrupalPublicStreamWrapper's getDirectoryPath() method, even when using a stream wrapper that inherits from DrupalPublicStreamWrapper. This means that you have to redefine getExternalUrl() in your custom stream wrapper class just to use your overridden getDirectoryPath() method.

This patch makes getExternalUrl() call the current instance's getDirectoryPath() method instead of DrupalPublicStreamWrapper's version of that method.