[boost] [test] patch to enable gcc visibility support

Hi ! I've attached a patch which uses the new Boost.Config logic introduced in revision 62140 to enable gcc visibility support. This fixes #2114 for Boost.Test. It is based on the already working patches to Boost.System and testet on gcc-4.4, 4.5 and msvc-9.0 and 10. Okay to commit ? Yours, Jürgen -- * Dipl.-Math. Jürgen Hunold ! Ingenieurgesellschaft für * voice: ++49 511 262926 57 ! Verkehrs- und Eisenbahnwesen mbH * fax : ++49 511 262926 99 ! Lister Straße 15 * juergen.hunold@ivembh.de ! www.ivembh.de * * Geschäftsführer: ! Sitz des Unternehmens: Hannover * Prof. Dr.-Ing. Thomas Siefer ! Amtsgericht Hannover, HRB 56965 * PD Dr.-Ing. Alfons Radtke !