Fix test mode and write to null

Fix test mode to not always return success.
Don't ask for permission to overwrite `nulmark`.

Before:

    > echo "hello world" > file
    > lz4 -t file
    successfully decoded 12 bytes
    > lz4 -tf file
    successfully decoded 12 bytes
    > lz4 file null
    Warning : /dev/null already exists
    Overwrite ? (Y/n) : n
    Error 12 : No. Operation aborted : /dev/null already exists
    > lz4 file /dev/null
    Warning : /dev/null already exists
    Overwrite ? (Y/n) : n
    Error 12 : No. Operation aborted : /dev/null already exists

After:

    > lz4 -t file
    Error 44 : Unrecognized header : file cannot be decoded
    > lz4 -tf file
    Error 44 : Unrecognized header : file cannot be decoded
    > lz4 file null
    Compressed 12 bytes into 31 bytes ==> 258.33%
    > lz4 file /dev/null
    Compressed 12 bytes into 31 bytes ==> 258.33%

1 files changed, 4 insertions, 0 deletions

diff --git a/programs/lz4io.h b/programs/lz4io.h
index 4f0e02a..8109298 100644
--- a/programs/lz4io.h
+++ b/programs/lz4io.h
@@ -63,6 +63,10 @@ int LZ4IO_decompressMultipleFilenames(const char** inFileNamesTable, int ifntSiz
    return : overwrite mode (0/1) */
 int LZ4IO_setOverwrite(int yes);
 
+/* Default setting : passThrough = 1;
+   return : passThrough mode (0/1) */
+int LZ4IO_setPassThrough(int yes);
+
 /* blockSizeID : valid values : 4-5-6-7
    return : -1 if error, blockSize if OK */
 int LZ4IO_setBlockSizeID(int blockSizeID);