Fix compile issues with new libpng versions and qt3 builds by using an older version of libpng. In libpng, make older versions available.

var/spack/repos/builtin/packages/libpng/package.py

@@ -8,6 +8,9 @@ class Libpng(Package):
     version('1.6.16', '1a4ad377919ab15b54f6cb6a3ae2622d')
     version('1.6.15', '829a256f3de9307731d4f52dc071916d')
     version('1.6.14', '2101b3de1d5f348925990f9aa8405660')
+    version('1.5.26', '3ca98347a5541a2dad55cd6d07ee60a9')
+    version('1.4.19', '89bcbc4fc8b31f4a403906cf4f662330')
+    version('1.2.56', '9508fc59d10a1ffadd9aae35116c19ee')
 
     depends_on('zlib')
 

var/spack/repos/builtin/packages/qt/package.py

@@ -29,7 +29,8 @@ class Qt(Package):
     depends_on("zlib")
     depends_on("dbus", when='@4:')
     depends_on("libtiff")
-    depends_on("libpng")
+    depends_on("libpng@1.2.56", when='@3')
+    depends_on("libpng", when='@4:')
     depends_on("libmng")
     depends_on("jpeg")
 
@@ -120,6 +121,8 @@ def common_config_args(self):
 
     @when('@3')
     def configure(self):
+        # An user report that this was necessary to link Qt3 on ubuntu
+        os.environ['LD_LIBRARY_PATH'] = os.getcwd()+'/lib' 
         configure('-prefix', self.prefix,
                   '-v',
                   '-thread',