Add some lossless h.264 encoding presets as suggested by Jason

Originally committed as revision 16478 to svn://svn.ffmpeg.org/ffmpeg/trunk

ffpresets/libx264-lossless_slow.ffpreset

@@ -0,0 +1,20 @@
+coder=1
+flags=+loop
+cmp=+chroma
+partitions=+parti8x8+parti4x4+partp8x8+partp4x4-partb8x8
+me_method=umh
+subq=6
+me_range=16
+g=250
+keyint_min=25
+sc_threshold=40
+i_qfactor=0.71
+b_strategy=1
+qcomp=0.6
+qmin=10
+qmax=51
+qdiff=4
+refs=2
+directpred=1
+flags2=+dct8x8+fastpskip
+cqp=0