vchoi_fork

[svn-r12890] Description:
    Finished implementation of H5Lget_info_by_idx for all cases: old vs. new
group formats, compact vs. dense new link storage, increasing vs. decreasing
vs. native iteration order.

    Also, refactor symbol table "foo by index" routines to be more generic
and share more code by using a single B-tree iteration callback which makes
callbacks to a specific "get <foo>" callback.

Tested on:
    Mac OS X/32 10.4.8 (amazon)
    FreeBSD/32 4.11 (sleipnir)
    Linux/32 2.4 (heping)
    Linux/64 2.4 (mir)
    AIX/32 5.? (copper)