hdf5

[svn-r20913] Issue 7579 - The overflowing ENUM values are inconsistent.  When no conversion is involved in reading or writing the 
data, overflowing values are retained.  When conversion happens, the values become -1. The conversion function puts -1
when overflow happens.  I added two new dataset transfer property to control whether to fill 0xff in the destination 
data or convert to the destination data when overflow happens.  The two new functions are H5Pset(get)_enum_conv_overflow.  I also added test cases in enum.c and dtypes.c.

Tested on jam, koala, and heiwa.