Change Texinfo output to UTF-8

Since the whole documentation tool chain is now UTF-8 and there is an
increasing number of non-ISO-8859-1 characters in the text, keeping
the Texinfo output in ISO 8859-1 just creates unnecessary
complications.  Depending on the platform, there are conversion
failures and thus build failures, or weirdly converted characters.  By
changing the output to UTF-8, the whole encoding conversion business
is sidestepped.

doc/src/sgml/Makefile

@@ -201,7 +201,7 @@ MAKEINFO = makeinfo
 	$(DB2X_XSLTPROC) -s texi -g output-file=$(basename $@) $< -o $@
 
 %.texi: %.texixml
-	$(DB2X_TEXIXML) --encoding=iso-8859-1//TRANSLIT $< --to-stdout > $@
+	$(DB2X_TEXIXML) --encoding=utf-8 $< --to-stdout > $@
 
 %.info: %.texi
 	$(MAKEINFO) --enable-encoding --no-split --no-validate $< -o $@