upgraded png version line 167 448

Makefile.am

@@ -24,6 +24,7 @@ ADD_LIBXMI =
 else
 ADD_LIBXMI = libxmi
 endif
+ACLOCAL_AMFLAGS = -I m4
 
 SUBDIRS = lib spline double ode ode-examples libplot $(ADD_LIBXMI) plot tek2plot plotfont graph hersheydemo $(ADD_LIBPLOTTER) include info doc fonts test
 

NEWS

@@ -1,3 +1,6 @@
+Jan 5, 2017
+Fixed bug when compiling against PNG version 1.6
+
 Version 2.6 released, 9/2009.  [Includes libplot 4.4, interface age=2.]
 
 ode:	 File ode/specfun.c now heavily rewritten to remove all non-GNU

README

@@ -420,3 +420,68 @@ The contents of the plotutils package are:
 	double. This is a filter for converting, scaling and cutting
 		unformatted (binary) or ASCII data streams.  It is still
 		under development and is not yet documented.
+
+Development headers needed
+
+On Centos systems:
+	Xlib.h in libX11-devel
+	Intrinsic.h in libXt-devel
+	libXaw-devel
+
+On ubuntu (use sudo apt-get install xxxx):
+	libx11-dev
+	libxt-dev
+	libxaw7-dev
+	libpng-dev, this may not bring to the latest version.
+	   A manual installation may be needed.
+
+	   if libpng is 1.2, then you need to do
+    libpng16-dev
+
+You will need makeinfo
+ which is part of texinfo
+
+sudo apt-get install texinfo
+
+
+
+To build the libplotter for the C++ interface
+configure --enable-libplotter     build the C++ Plotter class library and C++ software
+
+There is still a problem with PNG plotter header.  
+‘PNGPlotter’
+
+After installing the folliwng png libs, the package can be linked
+properly. We have made png mandatory instead of optional.
+-----------------------------------
+libpng-dev - PNG library - development (version 1.6)
+libpng++-dev - C++ interface to the PNG (Portable Network Graphics) library
+------------------------
+
+configure.ac  line 89 is obsolete, if remove it then ode/extern.h line 83
+will be a problem.
+----------------
+ 88 AC_TYPE_PID_T
+ 89 AC_TYPE_SIGNAL
+ 90 
+--------------------
+
+ode/extern.h
+82 struct sym * salloc (void);
+83 RETSIGTYPE fptrap (int sig);
+84 
+
+— Macro: AC_TYPE_SIGNAL
+
+    If signal.h declares signal as returning a pointer to a function returning void, define RETSIGTYPE to be void; otherwise, define it to be int. These days, it is portable to assume C89, and that signal handlers return void, without needing to use this macro or RETSIGTYPE.
+
+    When targetting older K&R C, it is possible to define signal handlers as returning type RETSIGTYPE, and omit a return statement:
+
+              RETSIGTYPE
+              hup_handler ()
+              {
+              ...
+              }
+
+So we will edite the source code to replace RETSIGTYPE with void
+Then comment out the AC_TYPE_SIGNAL macro