Fixed time and space usage in cases where entity references

follow each other (thanks to Ivan Shvedunov for the report).

	* xml/xml-parse.lisp (P/CONTENT): Removed useless call to append.
	Use loop instead of tail recursion.

xml/xml-parse.lisp

@@ -2800,19 +2800,17 @@
 
 (defun p/content (input)
   ;; [43] content ::= (element | CharData | Reference | CDSect | PI | Comment)*
+  (loop
      (multiple-value-bind (cat sem) (peek-token input)
        (case cat
 	 ((:stag :ztag)
-       (p/element input)
-       (p/content input))
+	  (p/element input))
 	 ((:CDATA)
 	  (process-characters input sem)
-       (sax:characters (handler *ctx*) sem)
-       (p/content input))
+	  (sax:characters (handler *ctx*) sem))
 	 ((:ENTITY-REF)
 	  (let ((name sem))
 	    (consume-token input)
-         (append
 	    (recurse-on-entity input name :general
 			       (lambda (input)
 				 (prog1
@@ -2821,24 +2819,20 @@
 				       (external-entdef (p/ext-parsed-ent input)))
 				   (unless (eq (peek-token input) :eof)
 				     (wf-error input "Trailing garbage. - ~S"
-					     (peek-token input))))))
-          (p/content input))))
+					       (peek-token input))))))))
 	 ((:<!\[)
 	  (let ((data (process-cdata-section input)))
 	    (sax:start-cdata (handler *ctx*))
 	    (sax:characters (handler *ctx*) data)
-	 (sax:end-cdata (handler *ctx*)))
-       (p/content input))
+	    (sax:end-cdata (handler *ctx*))))
 	 ((:PI)
 	  (consume-token input)
-       (sax:processing-instruction (handler *ctx*) (car sem) (cdr sem))
-       (p/content input))
+	  (sax:processing-instruction (handler *ctx*) (car sem) (cdr sem)))
 	 ((:COMMENT)
 	  (consume-token input)
-       (sax:comment (handler *ctx*) sem)
-       (p/content input))
+	  (sax:comment (handler *ctx*) sem))
 	 (otherwise
-       nil))))
+	  (return))))))
 
 ;; [78] extParsedEnt ::= TextDecl? contentw
 ;; [79]        extPE ::= TextDecl? extSubsetDecl