For some reason, in code dating to 2001, encoded jpeg buffers were
rounded up to multiples of 4 bytes.  With the added bonus that the
extra bytes are unwritten, causing valgrind issues.  Oops.  I can't
think of any reason why JPEG buffers need to be multiples of 4 bytes,
so I removed the padding.  There might be some code somewhere that
depends on this behavior, so if this needs to be reverted, please fix
the valgrind issues.