hdf5

[svn-r19808] Purpose:

    Add "--enable-unsupported" configure flag.

Description

    The "--enable-unsupported" configure flag allows a user to
    prevent configure from failing due to the use of incompatible
    options, such as c++ with parallel.

    Specifying --enable-unsupported will bypass all of configure's
    checks for incompatible and unsupported combinations of flags. 
    There are no guarantees that the library will be configured
    in any sort of working condition, but that's the risk of
    using the --enable-unsupported flag.

    I've changed all default error messages related to unsupported
    option combinations to indicate that using --enable-unsupported
    will allow configure to complete without error.

Tested:

    by hand on jam, tested all unsupported configure option 
    combinations with and without the new flag, making sure
    the flag allows configure to finish without error. 
    (h5committest wouldn't do any good here; it won't test
    the new option, and since we're enabling unsupported
    combinations, failures are likely to occur in build or
    tests with --enable-unsupported turned on anyways. 
    That's why they're unsupported!)