V3 Testsuite Patch: instantiations for bitmap_allocator tests

[Paolo Carlini]

Mark Mitchell wrote:

>Dave Anglin has reported some testsuite failures on AIX 4.3.3, which
>is a system without weak symbols.
>
Actually, this is probably my fault: recently in mainline I removed most
of those explicit memory allocation, definitely not needed anymore when
the default memory allocator is used (due to a mix of reasons, among
which the configury bits that only enable mt_allocator on selected
platforms).

However, an annoying special case here are the ext/*allocator tests
themselves, that in general test all the allocators on all the
platforms: maybe we have to readd a few explicit instantiations also
elsewhere, these changes are OK with me in advance.

Thanks,
Paolo.