exception safety validation

[François Dumont]

Hi

     I enhance scope of the small exception safety test framework used 
to validate different levels of exception safety through the containers 
operations. I have added calls to C++ methods 
emplace/emplace_front/emplace_back/emplace_hint in C++11.

     Doing so I start having propagation_consistency test for vector to 
fail. I finally realized that the problem was that the throw_value_limit 
used for this test had no move semantic. So the copy constructor and 
assignment operator was called sometimes throwing exceptions. In this 
case the Standard says that there is no strong exception safety guaranty 
explaining why the test was failing.

     To fix it I have added for the moment move semantic to the 
throw_value_base type so that it never throws. I had to remove the dg-do 
run { xfail } in the equivalent deque test that was surely failing for 
the same reason.

     Now I wonder if there is something in the Standard saying that move 
construct/assign shall never throw ? At least, on vector modifiers it is 
clearly said that if the move constructor throw it can have undefined 
behavior. If move construct/assign can throw then we might consider a 
way to control wether or not it will throw depending on the test. When 
testing vector and deque it shall not throw, when testing node based 
container it can throw. What do you think ?

     I also wonder what are all the try { ... } catch (const 
__gnu_cxx::forced_error&) { throw; } in safety.h for ? Is it to 
influence the exception callstack ?


François

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