allow compile against ICU 4.0 - needed to be able to link against osx provided libicucore.dylib

INSTALL

@@ -62,9 +62,9 @@ First, here is a quick list of the required software dependencies:
     - system
     - thread
     - filesystem
-    - regex (built against libicu >= 4.2)
+    - regex (optionally built with icu regex support)
     - python - required only for python bindings (see below)
-- libicu >= 4.2 - International Components for Unicode
+- libicu >= 4.0 - International Components for Unicode
 - libpng - PNG Graphics
 - libjpeg - JPEG Graphics
 - libtiff - TIFF Graphics 

SConstruct

@@ -809,7 +809,7 @@ int main()
         return False
     
     major, minor = map(int,result.split('.'))
-    if major >= 4 and minor >= 2:
+    if major >= 4 and minor >= 0:
         color_print(4,'\nFound icu version... %s\n' % result)
         return True
     

src/map.cpp

@@ -29,6 +29,9 @@
 #include <mapnik/hit_test_filter.hpp>
 #include <mapnik/scale_denominator.hpp>
 
+// icu
+#include <unicode/uversion.h>
+
 namespace mapnik
 {
 
@@ -653,7 +656,11 @@ void Map::init_metawriters()
 
 void Map::set_metawriter_property(std::string name, std::string value)
 {
+#if (U_ICU_VERSION_MAJOR_NUM > 4) || (U_ICU_VERSION_MAJOR_NUM == 4 && U_ICU_VERSION_MINOR_NUM >=2)
     metawriter_output_properties[name] = UnicodeString::fromUTF8(value);
+#else
+    metawriter_output_properties[name] = UnicodeString(value.c_str());
+#endif
 }
 
 std::string Map::get_metawriter_property(std::string name) const