Doc: hack table 13.2 "Conflicting Lock Modes" till it fits in PDF.

Doc: hack table 13.2 "Conflicting Lock Modes" till it fits in PDF.

I can't see any way to make this table fit in PDF column width
without either a fundamental redesign or abbreviating EXCLUSIVE.
So I did the latter.

It'd be nicer if the abbreviating didn't leak into the HTML output
as well; but the hackery required to make the output different
seems like more trouble than it's really worth.

Discussion: https://postgr.es/m/6916.1589146280@sss.pgh.pa.us