TODO revision 11293 
1Possible upgrades to gzfilebuf:
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3- The ability to do putback (e.g. putbackfail)
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5- The ability to seek (zlib supports this, but could be slow/tricky)
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7- Simultaneous read/write access (does it make sense?)
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9- Support for ios_base::ate open mode
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11- Locale support?
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13- Check public interface to see which calls give problems
14  (due to dependence on library internals)
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16- Override operator<<(ostream&, gzfilebuf*) to allow direct copying
17  of stream buffer to stream ( i.e. os << is.rdbuf(); )
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