Added test_rbyd_large with better boundary conditions near end-of-block

test_rbyd_large also doubles as a decent fuzz test, since it involves
many more tags than the permutation testing can ever hit.

lfs.h

@@ -84,6 +84,8 @@ enum lfs_error {
     LFS_ERR_NOMEM       = -12,  // No more memory available
     LFS_ERR_NOATTR      = -61,  // No data/attr available
     LFS_ERR_NAMETOOLONG = -36,  // File name too long
+    LFS_ERR_RANGE       = -7,   // Result out of range
+    // TODO should all overflow errors actually be corrupt errors?
     LFS_ERR_OVERFLOW    = -75,  // Value too large for defined data type
 };