Filter out warnings

[Matthew McMinn]

I'm working with a library written by someone else, and when I compile 
my code (which links to their library) I get a lot of the following warnings

warning: `pnl::GeneralAllocator<T>::size_type' is implicitly a typename

I realize that this code pattern is deprecated, but while they are 
working on updating their code, is there any way for me to filter those 
warnings out?  I've tried every combination of command line args into 
g++ I can think of to not show these warnings, and have had no luck.

Thanks

Matt