vchoi_fork

[svn-r12895] Description:
    Add new H5Lget_val_by_idx() routine & tests.

    Also includes most of changes for H5Ldelete_by_idx() routine.

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)