vchoi_fork

[svn-r4868] Purpose:
    Bug fixes

Description:
    This checkin addresses two separate bugs:
     #1 - When a compound datatype with a VL datatype as a field is used
            to read or write data, the datatype conversion paths added to
            the table of paths were treating the VL datatypes somewhat too
            genericly - they weren't dicriminating between VL datatypes used
            in different files and therefore there was the possibility that
            a path in the table having information for one file could get used
            with a second file, causing errors or core dumps (if the first
            file was closed before the later file used the path).
     #2 - When composite (compound, array or VL) datatype paths in the datatype
            conversion table are being tested to see if they can be used for
            the current datatypes being converted, they can cause additional
            conversion paths to be registered in the conversion path table.
            Since this causes the global table to change size and entries to
            move around, it is possible that the local variables tracking a
            potential path could become incorrect as the global table was
            changed out from underneath them.

    Both bugs fixed are described in bug #703

Solution:
    Two separate fixes:
     #1 - Changed H5T_cmp to differentiate between VL datatypes in different
            files and not to return datatypes in two different files as equal.
     #2 - Note size of global table before evaluating datatype paths.  Then,
            after the appropriate path has been chosen, check if the size of
            the global table has changed and recompute the position of the path
            chosen in the table if necessary.

Platforms tested:
    FreeBSD 4.5 (sleipnir)