_bfd_free_cached_info

_bfd_free_cached_info

doc/bfdint.texi and comments in the aout and som code about this
function are just wrong, and its name is not very apt.  Better would
be _bfd_mostly_destroy, and we certainly should not be saying anything
about the possibility of later recreating anything lost by this
function.  What's more, if _bfd_free_cached_info is called when
creating an archive map to reduce memory usage by throwing away
symbols, the target _close_and_cleanup function won't have access to
tdata or section bfd_user_data to tidy memory.  This means most of the
target _close_and_cleanup function won't do anything, and therefore
sometimes will result in memory leaks.

This patch fixes the documentation problems and moves most of the
target _close_and_cleanup code to target _bfd_free_cached_info.
Another notable change is that bfd_generic_bfd_free_cached_info is now
defined as _bfd_free_cached_info rather than _bfd_bool_bfd_true,
ie. the default now frees objalloc memory.