scons: add option to configure custom paths to ltdl - refs #1376

SConstruct

@@ -309,7 +309,9 @@ opts.AddVariables(
     PathVariable('ICU_LIBS','Search path for ICU include files','/usr/' + LIBDIR_SCHEMA_DEFAULT, PathVariable.PathAccept),
     ('ICU_LIB_NAME', 'The library name for icu (such as icuuc, sicuuc, or icucore)', 'icuuc'),
     PathVariable('PNG_INCLUDES', 'Search path for libpng include files', '/usr/include', PathVariable.PathAccept),
-    PathVariable('PNG_LIBS','Search path for libpng include files','/usr/' + LIBDIR_SCHEMA_DEFAULT, PathVariable.PathAccept),
+    PathVariable('PNG_LIBS','Search path for libpng library files','/usr/' + LIBDIR_SCHEMA_DEFAULT, PathVariable.PathAccept),
+    PathVariable('LTDL_INCLUDES', 'Search path for libltdl (part of libtool) include files', '/usr/include', PathVariable.PathAccept),
+    PathVariable('LTDL_LIBS','Search path for libltdl (ltdl.h) library files','/usr/' + LIBDIR_SCHEMA_DEFAULT, PathVariable.PathAccept),
     BoolVariable('JPEG', 'Build Mapnik with JPEG read and write support', 'True'),
     PathVariable('JPEG_INCLUDES', 'Search path for libjpeg include files', '/usr/include', PathVariable.PathAccept),
     PathVariable('JPEG_LIBS', 'Search path for libjpeg library files', '/usr/' + LIBDIR_SCHEMA_DEFAULT, PathVariable.PathAccept),
@@ -1055,7 +1057,7 @@ if not preconfigured:
 
     # Adding the required prerequisite library directories to the include path for
     # compiling and the library path for linking, respectively.
-    for required in ('PNG', 'JPEG', 'TIFF','PROJ','ICU', 'SQLITE'):
+    for required in ('PNG', 'JPEG', 'TIFF','PROJ','ICU', 'SQLITE', 'LTDL'):
         inc_path = env['%s_INCLUDES' % required]
         lib_path = env['%s_LIBS' % required]
         env.AppendUnique(CPPPATH = os.path.realpath(inc_path))