only build geojson plugin if >= boost 1.47 is available to avoid potential compiler errors with missing boost/geometry headers if people try to force older boost versions

plugins/input/geojson/build.py

@@ -19,20 +19,27 @@
 #
 
 
-Import ('plugin_base')
 Import ('env')
 
+can_build = False
+
+if env.get('BOOST_LIB_VERSION_FROM_HEADER'):
+    boost_version_from_header = int(env['BOOST_LIB_VERSION_FROM_HEADER'].split('_')[1])
+    if boost_version_from_header >= 47:
+        can_build = True
+
+if not can_build:
+    print 'WARNING: skipping building the optional geojson datasource plugin which requires boost >= 1.47'
+else:
+    Import ('plugin_base')
     prefix = env['PREFIX']
-
     plugin_env = plugin_base.Clone()
-
     geojson_src = Split(
       """
       geojson_datasource.cpp
       geojson_featureset.cpp
       """
             )
-
     libraries = []
     # Link Library to Dependencies
     libraries.append('mapnik')