Tidy up "diag_tables.php" XHTML

Add BODY tag
Add ACTION to FORM tag
Add CDATA section to SCRIPTS
Remove NAME from OPTION tag, not valid in XHTML
Update HTML Boolean operators
Add SUMMARY to TABLE
Close IMG tag and add ALT
Move closing Anchor tag into PHP staement
Change Paragraph tag to TR tag and close
Update non breaking space tag
Add missing closing FORM, closing BODY and closing HTML tags