[boost] Modularizing explicit-failures-markup.xml

Hi, I'm looking into implementing a mechanism for updating explicit-failures-markup.xml without updating the super project. My basic idea is that modules can have a 'status/explicit-failures-markup.xml' file, and I'll write a script to update the super project file from modules. It will have the same format as the super project file, so can just copy and paste the relevant parts into your module. Does that sound okay? It might be better if the regression scripts handled this themselves, but I'm not sure if anyone would be available to implement that. Daniel