hdf5_ep

Merge pull request #502 in HDFFV/hdf5 from ~BMRIBLER/hdf5_1_8_bmr:hdf5_1_8 to hdf5_1_8

* commit '8b1a53896565cafca3795d139a37148f89bf928d':
  Add H5Lexists wrappers Description:     Added wrappers H5Location::exists() for H5Lexists.     Added new class LinkAccPropList to be used by H5Location::exists()     Rearranged source files in Makefile.am Platforms tested:     Linux/32 2.6 (jam)     Linux/64 (platypus)     Darwin (osx1010test)
  Improvement of class hierarchy Description:     - Moved class Attribute to be derived from class H5Location instead of       IdComponent because an attribute id can be used as loc_id in C APIs.     - Copied wrappers of H5A APIs in H5Location into H5Object because H5A       functions do not take an attribute id as loc_id.  The original wrappers       will be deprecated in future releases.     - Revised comments Platforms tested:     Linux/32 2.6 (jam)     Linux/64 (platypus)     Darwin (osx1010test)