bitcost: fix bitcost() function, broken 13 months ago by 07015bbe306b

when bitcost() was first introduced, we had two competing table formats for the
s_bitsizes[] array. Eventually the x264 style array won out, but this function
was not updated.

This bug was almost harmless, bitcost() could still evaluate differences in bit
costs correctly, but the upshift caused read bound exceptions when the motion
vectors became close to the HEVC max of 4k.

--HG--
branch : stable
extra : amend_source : 7b4c7a3f24d90a60081ad18319ba0725c1f71d0c
bitcost: increase size of cost arrays, for pessimal situations

MVD is MV minus MVP. MV could be BC_MAX_MV and MVP could be -BC_MAX_MV

--HG--
branch : stable
extra : rebase_source : 64e4bb5f652018675e8ccea30b491e9843437222