This patch makes all targets (except the remote target, which will be
done later in the series) manage the inferior table.  For most targets,
there will ever only be one entry in the table, until they gain support
for multi-process.

Will notice that this colides a bit with the linux-fork.c list of
forks.  Over time, I'd like to migrate "info forks" functionality
into the common inferior list.  For now, inferiors are listed in
both lists.

-- 
Pedro Alves