. moved swab32 from input_ext-dec.h to common.h. We probably won't need
   it anymore really soon, since ntohl() and htonl() seem to be properly
   optimized when gcc is passed the right optimization flags.

 . fixed GetBits32 and RemoveBits32. I know the #ifdefs are useless since
   we only support u32 words, but it's a safe reminder. Comments appreciated
   on this fix since I may have b0rked something -- it runs well here though.