yv12extend: name variables consistently
yv12extend: name variables consistently

- s|source -> src
- dest -> dst
- use verbose names in extend_plane dropping the redundant comments

+ light cosmetics:
- join a few lines / assignments
- drop some unnecessary comments & includes

Change-Id: I6d979a85a0223a0a79a22f79a6d9c7512fd04532

iniwf/webm.libvpx,Distrotech/libvpx,cinema6/libvpx,shyamalschandra/libvpx,stewnorriss/libvpx,Topopiccione/libvpx,altogother/webm.libvpx,webmproject/libvpx,kleopatra999/webm.libvpx,lyx2014/libvpx_c,reimaginemedia/webm.libvpx,pcwalton/libvpx,jacklicn/webm.libvpx,abwiz0086/webm.libvpx,goodleixiao/vpx,mwgoldsmith/vpx,lyx2014/libvpx_c,smarter/aom,jmvalin/aom,altogother/webm.libvpx,shyamalschandra/libvpx,luctrudeau/aom,jmvalin/aom,running770/libvpx,altogother/webm.libvpx,kleopatra999/webm.libvpx,kalli123/webm.libvpx,luctrudeau/aom,turbulenz/libvpx,jdm/libvpx,webmproject/libvpx,hsueceumd/test_hui,abwiz0086/webm.libvpx,turbulenz/libvpx,ShiftMediaProject/libvpx,zofuthan/libvpx,mbebenita/aom,openpeer/libvpx_new,stewnorriss/libvpx,hsueceumd/test_hui,pcwalton/libvpx,kim42083/webm.libvpx,stewnorriss/libvpx,matanbs/vp982,gshORTON/webm.libvpx,matanbs/vp982,Topopiccione/libvpx,cinema6/libvpx,pcwalton/libvpx,turbulenz/libvpx,smarter/aom,GrokImageCompression/aom,abwiz0086/webm.libvpx,jmvalin/aom,turbulenz/libvpx,felipebetancur/libvpx,liqianggao/libvpx,Suvarna1488/webm.libvpx,openpeer/libvpx_new,zofuthan/libvpx,lyx2014/libvpx_c,Distrotech/libvpx,Laknot/libvpx,turbulenz/libvpx,ittiamvpx/libvpx,matanbs/vp982,mwgoldsmith/libvpx,n4t/libvpx,shyamalschandra/libvpx,thdav/aom,shareefalis/libvpx,mwgoldsmith/vpx,liqianggao/libvpx,reimaginemedia/webm.libvpx,VTCSecureLLC/libvpx,reimaginemedia/webm.libvpx,kim42083/webm.libvpx,ittiamvpx/libvpx-1,Acidburn0zzz/webm.libvpx,sanyaade-teachings/libvpx,Maria1099/webm.libvpx,WebRTC-Labs/libvpx,cinema6/libvpx,mwgoldsmith/vpx,lyx2014/libvpx_c,smarter/aom,mwgoldsmith/vpx,n4t/libvpx,kim42083/webm.libvpx,jdm/libvpx,Distrotech/libvpx,shacklettbp/aom,Topopiccione/libvpx,liqianggao/libvpx,Laknot/libvpx,mwgoldsmith/vpx,matanbs/webm.libvpx,Suvarna1488/webm.libvpx,charup/https---github.com-webmproject-libvpx-,thdav/aom,jdm/libvpx,WebRTC-Labs/libvpx,luctrudeau/aom,n4t/libvpx,liqianggao/libvpx,zofuthan/libvpx,ittiamvpx/libvpx,mwgoldsmith/libvpx,VTCSecureLLC/libvpx,webmproject/libvpx,liqianggao/libvpx,pcwalton/libvpx,ittiamvpx/libvpx-1,Maria1099/webm.libvpx,ShiftMediaProject/libvpx,sanyaade-teachings/libvpx,Acidburn0zzz/webm.libvpx,turbulenz/libvpx,reimaginemedia/webm.libvpx,shareefalis/libvpx,ittiamvpx/libvpx-1,GrokImageCompression/aom,Suvarna1488/webm.libvpx,pcwalton/libvpx,jmvalin/aom,running770/libvpx,charup/https---github.com-webmproject-libvpx-,abwiz0086/webm.libvpx,webmproject/libvpx,mwgoldsmith/libvpx,luctrudeau/aom,kalli123/webm.libvpx,ittiamvpx/libvpx,Suvarna1488/webm.libvpx,iniwf/webm.libvpx,stewnorriss/libvpx,jdm/libvpx,hsueceumd/test_hui,mbebenita/aom,jacklicn/webm.libvpx,jmvalin/aom,ShiftMediaProject/libvpx,altogother/webm.libvpx,turbulenz/libvpx,sanyaade-teachings/libvpx,jacklicn/webm.libvpx,felipebetancur/libvpx,lyx2014/libvpx_c,kleopatra999/webm.libvpx,abwiz0086/webm.libvpx,hsueceumd/test_hui,zofuthan/libvpx,goodleixiao/vpx,GrokImageCompression/aom,Laknot/libvpx,WebRTC-Labs/libvpx,Laknot/libvpx,gshORTON/webm.libvpx,gshORTON/webm.libvpx,mwgoldsmith/vpx,matanbs/vp982,openpeer/libvpx_new,jacklicn/webm.libvpx,sanyaade-teachings/libvpx,shacklettbp/aom,kim42083/webm.libvpx,ittiamvpx/libvpx,VTCSecureLLC/libvpx,Topopiccione/libvpx,GrokImageCompression/aom,jdm/libvpx,turbulenz/libvpx,thdav/aom,kleopatra999/webm.libvpx,webmproject/libvpx,Distrotech/libvpx,shareefalis/libvpx,ittiamvpx/libvpx-1,matanbs/vp982,Acidburn0zzz/webm.libvpx,Acidburn0zzz/webm.libvpx,Distrotech/libvpx,matanbs/webm.libvpx,kalli123/webm.libvpx,mwgoldsmith/libvpx,luctrudeau/aom,goodleixiao/vpx,webmproject/libvpx,running770/libvpx,mwgoldsmith/libvpx,hsueceumd/test_hui,thdav/aom,n4t/libvpx,liqianggao/libvpx,Maria1099/webm.libvpx,ittiamvpx/libvpx-1,mbebenita/aom,matanbs/webm.libvpx,thdav/aom,n4t/libvpx,jacklicn/webm.libvpx,Acidburn0zzz/webm.libvpx,altogother/webm.libvpx,mbebenita/aom,cinema6/libvpx,felipebetancur/libvpx,ittiamvpx/libvpx-1,VTCSecureLLC/libvpx,iniwf/webm.libvpx,matanbs/vp982,Maria1099/webm.libvpx,GrokImageCompression/aom,mbebenita/aom,altogother/webm.libvpx,ShiftMediaProject/libvpx,matanbs/vp982,goodleixiao/vpx,smarter/aom,shareefalis/libvpx,openpeer/libvpx_new,hsueceumd/test_hui,abwiz0086/webm.libvpx,kalli123/webm.libvpx,iniwf/webm.libvpx,Acidburn0zzz/webm.libvpx,shacklettbp/aom,luctrudeau/aom,lyx2014/libvpx_c,Distrotech/libvpx,pcwalton/libvpx,iniwf/webm.libvpx,VTCSecureLLC/libvpx,charup/https---github.com-webmproject-libvpx-,matanbs/webm.libvpx,goodleixiao/vpx,mbebenita/aom,shacklettbp/aom,jmvalin/aom,mbebenita/aom,Laknot/libvpx,thdav/aom,charup/https---github.com-webmproject-libvpx-,ittiamvpx/libvpx,shyamalschandra/libvpx,jacklicn/webm.libvpx,cinema6/libvpx,kleopatra999/webm.libvpx,kalli123/webm.libvpx,kleopatra999/webm.libvpx,turbulenz/libvpx,Maria1099/webm.libvpx,shyamalschandra/libvpx,charup/https---github.com-webmproject-libvpx-,smarter/aom,Suvarna1488/webm.libvpx,kalli123/webm.libvpx,Topopiccione/libvpx,goodleixiao/vpx,cinema6/libvpx,shyamalschandra/libvpx,felipebetancur/libvpx,mbebenita/aom,Maria1099/webm.libvpx,reimaginemedia/webm.libvpx,reimaginemedia/webm.libvpx,ShiftMediaProject/libvpx,mbebenita/aom,gshORTON/webm.libvpx,charup/https---github.com-webmproject-libvpx-,Laknot/libvpx,openpeer/libvpx_new,zofuthan/libvpx,WebRTC-Labs/libvpx,matanbs/webm.libvpx,shacklettbp/aom,ittiamvpx/libvpx,shareefalis/libvpx,mwgoldsmith/libvpx,openpeer/libvpx_new,cinema6/libvpx,smarter/aom,zofuthan/libvpx,shacklettbp/aom,GrokImageCompression/aom,kim42083/webm.libvpx,Suvarna1488/webm.libvpx,felipebetancur/libvpx,running770/libvpx,gshORTON/webm.libvpx,Topopiccione/libvpx,shareefalis/libvpx,jdm/libvpx,stewnorriss/libvpx,VTCSecureLLC/libvpx,matanbs/webm.libvpx,running770/libvpx,iniwf/webm.libvpx,kim42083/webm.libvpx,stewnorriss/libvpx,WebRTC-Labs/libvpx,felipebetancur/libvpx,sanyaade-teachings/libvpx,gshORTON/webm.libvpx,running770/libvpx