...otherwise, at least with some --with-system-boost versions and C++11
compilers, like with Fedora's boost-1.50.0-4.fc18.x86_64 and
gcc-c++-4.7.2-8.fc18.x86_64, using this to copy-construct an instance of
boost::unordered::detail::ptr_node<std::pair<rtl::OUString,Bootstrap_Impl*>> in
the call to p_bootstrap_map->insert(...) in rtl_bootstrap_args_open
(sal/rtl/source/bootstrap.cxx) would memcopy the ptr_node and fail to call
rtl_uString_acquire, leading to memory corruption later on when
rtl_uString_release is called one time too often.

It is not entirely clear to me whether this is a shortcoming of the given Boost
version, but this patch solves the problem and brings rtl::Allocator::construct
in line with the (changed) Allocator requirements of C++11 anyway.

The problem potentially lurks with every use of rtl::Allocator, but only showed
now begining with LO 4.0 where e5111574 "Revert
'sb140: sb140: #i116981# clean up memory upon exit'" re-introduced code into
rtl_bootstrap_args_open that inserts into a boost::unordered_map that uses
rtl::Allocator.

Change-Id: I3be22f59a8eb49d31458480c27f3ce15803c7fd4