make compile of svg renderer optional (but on by default)

SConstruct

@@ -290,6 +290,8 @@ opts.AddVariables(
     # Variables affecting rendering back-ends
     BoolVariable('INTERNAL_LIBAGG', 'Use provided libagg', 'True'),
     
+    BoolVariable('SVG_RENDERER', 'build support for native svg renderer', 'True'),
+    
     # Variables for optional dependencies
     # Note: cairo, cairomm, and pycairo all optional but configured automatically through pkg-config
     # Therefore, we use a single boolean for whether to attempt to build cairo support.
@@ -1266,6 +1268,8 @@ if not HELP_REQUESTED:
     
     # build C++ tests
     SConscript('tests/cpp_tests/SConscript')
+    
+    if env['SVG_RENDERER']:
         SConscript('tests/cpp_tests/svg_renderer_tests/SConscript')
 
     # install pkg-config script and mapnik-config script

src/SConscript

@@ -186,7 +186,7 @@ elif env['XMLPARSER'] == 'libxml2' and env['HAS_LIBXML2']:
             source.remove(cpp)
         source.insert(0,env2.SharedObject(cpp))
 
-if True: # svg backend
+if ['SVG_RENDERER']: # svg backend
     source += Split(
         """
 	svg/svg_renderer.cpp