added buffer_get_chunk_tobuf() which copies some chunk from one buffer to the other without a temporary variable
fixed pcp_unpadfour() which didn't work at all (!!!)
added tests/pipetest.c so I can test pcpstream with armoring with various blocksizes
fixed ps_eof(): consider cache. fixed ps_read_cached() which didn't work under certain circumstances (blocksize < readbytes and such)