Add Polymorphic Memory Resource utilities and rework the separately compiled library:

- Dlmalloc's based C function are boost_cont_xxx no longer exported, but wrapped into C++ linkage dlmalloc_xxx functions to effectively reuse Boost's dynamic library and autolink machinery instead of rewriting machinery to compile the C source file.
- Refactored scoped_allocator_adaptor's construct logic as it was shared with polymorphic allocator's one. Moved common logic to detail/dispatch_uses_allocator.hpp. Refactored also scoped_allocator_adaptor test utilities to be reused with polymorphic_allocator tests.

build/Jamfile.v2

@@ -11,11 +11,8 @@ project boost/container
       <link>static:<define>BOOST_CONTAINER_STATIC_LINK=1
     ;
 
-# Base names of the source files for libboost_container
-CPP_SOURCES = alloc_lib ;
-
 lib boost_container
-   : $(CPP_SOURCES).c
+   : alloc_lib.c [ glob *.cpp ]
    : <link>shared:<define>BOOST_CONTAINER_DYN_LINK=1
      <link>static:<define>BOOST_CONTAINER_STATIC_LINK=1
    ;