dlopen vs. libstdc++, need entry in FAQ?

[Benjamin Kosnik]

Hey y'all. There seems to be a large number of dlopen-type questions
regarding libstdc++-v3. There is also a historical pattern of these
kinds of questions.

In particular, 

libstdc++/6062
libstdc++/5166

Both of these work, so I don't think I see any bugs. However, it might
be a good idea to put in some kind of documentation on how to properly
do this.

Also, it might be a good idea to actually test to see if this works in
the libstdc++ testsuite. Thoughts? Obviously, there are some problems
in that doing this in a portable manner is hard. Have other libraries attempted
something similar? If so, how is it done?

-benjamin