postgres.txt should get cleaned by 'make clean'.

doc/src/sgml/Makefile

@@ -2,7 +2,7 @@
 #
 # PostgreSQL documentation makefile
 #
-# $PostgreSQL: pgsql/doc/src/sgml/Makefile,v 1.147 2010/06/12 17:17:25 momjian Exp $
+# $PostgreSQL: pgsql/doc/src/sgml/Makefile,v 1.148 2010/06/12 21:40:31 tgl Exp $
 #
 #----------------------------------------------------------------------------
 
@@ -359,8 +359,8 @@ clean:
 # text --- these are shipped, but not in this directory
 	rm -f INSTALL HISTORY regress_README
 	rm -f INSTALL.html HISTORY.html regress_README.html
-# other HTML
-	rm -f postgres.html
+# single-page output
+	rm -f postgres.html postgres.txt
 # print
 	rm -f *.rtf *.tex-ps *.tex-pdf *.dvi *.aux *.log *.ps *.pdf *.out *.fot
 # index