[liblo] lo_send argument markers broke 64-bit ABI compatibility

Hi list,

So I finally located an actual ABI incompatibility due to 64-bit-ness
that was introduced post 0.26.

In commit 9adc42b111, a bug in using the LO_MARKER_A/B scheme to check
for unmatched arguments at the end of the lo_send() call was changed
to fix problems with 64-bit.  The LO_MARKER_A/B constants were
extended to 64-bit values.

Unfortunately, code that was not re-compiled against 0.27 that called
lo_send() broke after this change, since the LO_MARKER_A/B constants
are hard-coded into the calling code.  I have verified that swapping
out the liblo binary for 0.27 when running Ardour generates a message
"mismatching types and data".  Changing the LO_MARKERs back to their
previous values avoids this error message.

Camille, do you recall whether this commit actually fixed a bug (as
noted in the commit comment), or was it just precautionary?  If the
latter, do you think it's safe to change it back?

Steve