(1) Key frame: skip filter intra modes whose directional pred
    version is relatively bad (rd >= 1.125 * best_rd)
(2) Inter frame: do not check filter intra modes if best_intra_rd
    >= 1.25 * best_rd

Encoding time overhead is reduced by:
4.9% (9.2%->4.3%, soccer_cif)
Coding gains drop by 0.021% on lowres and by 0.076% on midres

Change-Id: I29b6f7d3d3dc4b362c6d63bc447e6a429ba5dc66