[boost] Compile fix for Boost.Test for aCC on HP-UX

Hello, you can find a small fix for boost/test/detail/basic_cstring/basic_cstring.hpp attached and a dirty workaround for a compiler bug in aCC for boost/test/unit_test_suite.hpp. As of the latter; the compiler seems to get confused by equal names in different namespaces and classes; renaming Impl helps or making the previous structure friend helps too (this I chose to minimize the change). Ferda HP-UX B.11.11 U 9000/800 aCC: HP ANSI C++ B3910B A.03.37 <<basic_cstring.hpp.diff>>