Reloading shader triggers numerous changed() and does not work

I've a shader whose source is a `File` (obtained via `Shader::sourceFromFile`).
If I want to update it, I'm calling `File::reload`. This does not work.
The sequence of operation that this causes is this:

1. `reload` call `changed` (once),
2. This calls `Shader::notifyChanged` that calls `updateSource`
3. This calls `File::string` and this triggers `File::loadFromFileContent` (so far, so good)
4. This then calls `Shader::invalidate` that sets compile flags to false
5. This calls `Shader::changed` and this triggers `Program::invalidate`
6. This set the dirty flag

[Later on, code that `use` program does this:]

1. In `Program::use` it's calling `checkDirty` (which is true)
2. It calls `Program::link` that's not compiling the shaders (but re-linking old compiled shaders)

Solution:
Compile shaders when the program is dirty (seems logical, not all user have a NVidia card that compile shaders when told to link them). Please notice that `Program::compileAttachedShaders` is protected and thus, not callable from user code. We can still call `Shader::compile` but this forces to keep a pointer on the shader (and that's exactly what `Program` is now doing, right?)

Also, I think there is too much abuse of the `ChangeListener` pattern here so the system is convoluted with many boolean to keep track of states. It would be so much easier if the Program was a listener of the Shader's AbstractStringSource directly, since the double listener triggering is useless in that case.
The only thing that can be modified in a Shader is its source. So why should they be in the Listener callchain instead of the source itself? Typically, `Shader::updateSource` or `invalidate` is misleading, since it does not cause reloading the source's text from the AbstractStringSource.

BTW, the error return is not checked in `Shader::updateSource` implementation, thus any error in the shader code will get silenced is using `reload` feature (at `ShadingLanguageIncludeImplementation_ShadingLanguageIncludeARB.cpp` line 26).
I guess you should check it explicitely in `updateSources` and throw a message upon error.
Or, if the Program is compiling the shader automatically, you'll get the error at that time, that's a good workaround too.

Verfolge den Reload-Pfad durch File::reload, Shader::notifyChanged, Shader::updateSource, Shader::invalidate, Program::invalidate und Program::use/checkDirty/link. Untersuche Program::compileAttachedShaders und ShadingLanguageIncludeImplementation_ShadingLanguageIncludeARB.cpp in Zeile 26 und reproduziere anschließend das Verhalten beim Neuladen von Shadern. Als abgeschlossen gilt die Aufgabe, wenn als dirty markierte Programme aktualisierte Shader vor dem erneuten Linken kompilieren und Fehler bei der Shader-Aktualisierung nicht stillschweigend ignoriert werden.

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