1. remove erroneously committed *.orig
2. fix LZ4 detection on Mac OS X and FreeBSD. Cannot do

   pkg_check_modules(LIBLZ4 liblz4)
   find_library(LIBLZ4_LIBS ... )

because find_library(X) does not do anything if X is defined (documented),
and pkg_check_modules(Y) sets Y_LIBS to "" (undocumented!)