Fixed bootloader on AIX for loading libpython.

On AIX the define `_ALL_SOURCE` must be set in order for the `dlopen()`
flag `RTLD_MEMBER` to be defined. This flag is necessary to load a shared
object from an archive.

Also, the special format `/path/to/archive.a(archive.so)` must be used
to reference the shared object.

This fixes ticket 1044 'AIX support broken in version 2.1'.