hdf5_msb

[svn-r24171] Purpose: Fix problem with gcc 4.8

Description:
With optimization enabled, gcc 4.8 inserts garbage into the padding bytes of
floating point types when assigning from a literal constant.  This caused
problems when H5detect.c scanned the bits in floating point types to determine
their properties.

Modified H5detect.c to scan for padding before further analyzing the type, and
to ignore all information in the padding areas.  Also removed code that
temporarily disabled optimization.

Tested: jam, koala, ostrich, platypus (h5committest)