hdf5_ep

[svn-r7829] Purpose:
    Bug fix & code cleanup

Description:
    Allowing the library to call malloc with a size of 0 bytes causes problems
for some users, so we check for allocations of 0 bytes and disallow them now.

    Cleaned up some code which could call malloc with 0 size.

    Changed some code calling HDmalloc directly to call H5MM_malloc(), which
allows us to check for 0 sized allocations.

Platforms tested:
    FreeBSD 4.9 (sleipnir)
    too minor to require h5committest