Description:
    Add new warning flags for gcc 4.9.x

Tested on:
    MacOSX/64 10.9.3 (amazon) w/gcc 4.9.0


git-svn-id: https://svn.hdfgroup.uiuc.edu/hdf5/trunk@25206 dab4d1a6-ed17-0410-a064-d1ae371a2980