HDF5 will use the C99 standard compiler whenever available but will
keep the library source C89 compatible.  C89 compatible means a standard
C89 compiler will compile the HDF5 source correctly though some non-C89
features (e.g., long double datatype) may not be available.

New features in C99 (e.g., newer datatypes) will not be all incorporated
into the HDF5 library at once.  They will be considered case by case
depending on needs and resources.


Reasons:
1) We are using some C99 features (e.g., long long) already in order to
   support 64 bits file size calculations.  Many compilers support the
   features but gives lots of warning messages if C99 standard option
   is not specified.  Turning on the C99 standard option will reduce
   those messages, making it much easier to catch the other warnings.

2) Start using "real" C89 standard compiler to prepare us to migrate
   to the newer standard eventually.

Concerns:
1) how to verify the library source is "C89 compatible"?
   Maybe something like, "./configure --enable-c89compat" will
   reset $CFLAGS to '-ansi'??

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Revised: AKC 2004/12/13