Since rangecoder is just a bunch of C functions, move it into the one user
(decompress_unlzma.c).  Also a slight #include cleanup, and I've been meaning
to put #include <unistd.h> into libbb.h since it's so darn common...
diff --git a/include/libbb.h b/include/libbb.h
index bc886da..998bcc6 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -24,6 +24,7 @@
 #include <sys/time.h>
 #include <sys/types.h>
 #include <termios.h>
+#include <unistd.h>
 
 #ifdef CONFIG_SELINUX
 #include <selinux/selinux.h>