sgml cleanup: unescaped '>' characters

I found myself rewriting the ./src/tools/find_gt_lt script in Perl
this evening, since the existing script was quite broken (the main
problem is it's not capable of understanding CDATA or sgml comment
sections, and hence produces a bunch of noise).

The rewritten version picked up a few stylistic inconsistencies in the
SGML, such as:
* breaking the trailing '>' of an SGML marker across lines. AFAIK
this is legal, but is a bit inconsistent and just confuses simplistic
tools like find_gt_lt
* using single quotes instead of double quotes to surround a node
attribute, as in <orderedlist numeration='loweralpha'>

as well as seemingly-invalid SGML, such as using '>' unescaped inside
normal SGML entries.

I've attached a patch to fix these problems. I can send in the new
version of find_gt_lt if these changes prove useful.

Josh