[NeXus-tech] flush in hdf4

[Paul Kienzle]

Hi,

After many hours I managed to build and test the new napi on OS X for  
HDF4/5/xml.

The storage size is now used by the python bindings when putting  
character data rather than the length of the stored data.  In the  
process of fixing this I cleaned up a dangling pointer reference.   
Between these, I hope the python wrapper is now stable, and #162 can  
be closed.

A separate issue I fixed in the python bindings was to force a close  
data for each open data. Otherwise, the path we are maintaining on  
the python side gets confused.

An unresolved issue is that HDF4 but not HDF5 or XML closes the  
currently open data group on NXflush.  I noticed this because I was  
interleaving flush class with putslab calls.  This wasn't caught  
before because the opendata call was in the loop with putslab.  This  
behaviour isn't documented.

I was unable to build and test under windows+mingw, and didn't try  
linux.  Can someone please run "python nxstest hdf4 hdf5 xml" on  
these two platforms?

Thanks,

   - Paul