[libpng16] Fix links in man page

libpng-manual.txt

@@ -70,12 +70,13 @@ a W3C Recommendation and as an ISO Standard (ISO/IEC 15948:2004 (E)) at
 The W3C and ISO documents have identical technical content.
 
 The PNG-1.2 specification is available at
-<http://www.libpng.org/pub/png/documents/>.  It is technically equivalent
+<http://png-mng.sourceforge.net/pub/png/spec/1.2/>.
+It is technically equivalent
 to the PNG specification (second edition) but has some additional material.
 
-The PNG-1.0 specification is available
-as RFC 2083 <http://www.libpng.org/pub/png/documents/> and as a
-W3C Recommendation <http://www.w3.org/TR/REC-png-19961001/>.
+The PNG-1.0 specification is available as RFC 2083 
+<http://png-mng.sourceforge.net/pub/png/spec/1.0/> and as a
+W3C Recommendation <http://www.w3.org/TR/REC-png-961001>.
 
 Some additional chunks are described in the special-purpose public chunks
 documents at <http://www.libpng.org/pub/png/documents/>.

libpng.3

@@ -578,12 +578,13 @@ a W3C Recommendation and as an ISO Standard (ISO/IEC 15948:2004 (E)) at
 The W3C and ISO documents have identical technical content.
 
 The PNG-1.2 specification is available at
-<http://www.libpng.org/pub/png/documents/>.  It is technically equivalent
+<http://png-mng.sourceforge.net/pub/png/spec/1.2/>.
+It is technically equivalent
 to the PNG specification (second edition) but has some additional material.
 
-The PNG-1.0 specification is available
-as RFC 2083 <http://www.libpng.org/pub/png/documents/> and as a
-W3C Recommendation <http://www.w3.org/TR/REC-png-19961001/>.
+The PNG-1.0 specification is available as RFC 2083 
+<http://png-mng.sourceforge.net/pub/png/spec/1.0/> and as a
+W3C Recommendation <http://www.w3.org/TR/REC-png-961001>.
 
 Some additional chunks are described in the special-purpose public chunks
 documents at <http://www.libpng.org/pub/png/documents/>.