scons: trunk requires at least icu 4.2, so enforce that at configure time - closes #482

INSTALL

@@ -62,10 +62,10 @@ First, here is a quick list of the required software dependencies:
     - system
     - thread
     - filesystem
-    - regex
+    - regex (built against libicu >= 4.2)
     - iostreams
     - python - required only for python bindings (see below)
-- libicu >= 1.4- International Components for Unicode
+- libicu >= 4.2 - International Components for Unicode
 - libpng - PNG Graphics
 - libjpeg - JPEG Graphics
 - libtiff - TIFF Graphics 

SConstruct

@@ -735,6 +735,33 @@ int main()
     major_version = version / 100000
     return [major_version,minor_version,patch_level]
 
+def icu_at_least_four_two(context):
+    ret = context.TryRun("""
+
+#include <unicode/uversion.h>
+#include <iostream>
+
+int main() 
+{
+    std::cout << U_ICU_VERSION_MAJOR_NUM << "." << U_ICU_VERSION_MINOR_NUM << std::endl;
+    return 0;
+}
+
+""", '.cpp')
+    # hack to avoid printed output
+    context.Message('Checking for ICU version >= 4.2... ')
+    #context.did_show_result=1
+    result = ret[1].strip()
+    if not result:
+        context.Result('error, could not get major and minor version from unicode/uversion.h')
+        return False
+    
+    color_print(4,'\nFound icu version... %s' % result)
+    major, minor = map(int,result.split('.'))
+    if major >= 4 and minor >= 2:
+        return True
+    return False
+    
 conf_tests = { 'prioritize_paths'      : prioritize_paths,
                'CheckPKGConfig'        : CheckPKGConfig,
                'CheckPKG'              : CheckPKG,
@@ -744,9 +771,10 @@ conf_tests = { 'prioritize_paths' : prioritize_paths,
                'GetMapnikLibVersion'   : GetMapnikLibVersion,
                'parse_config'          : parse_config,
                'parse_pg_config'       : parse_pg_config,
-               'ogr_enabled': ogr_enabled,
+               'ogr_enabled'           : ogr_enabled,
-               'get_pkg_lib': get_pkg_lib,
+               'get_pkg_lib'           : get_pkg_lib,
-               'rollback_option': rollback_option
+               'rollback_option'       : rollback_option,
+               'icu_at_least_four_two' : icu_at_least_four_two
                }
 
 
@@ -903,6 +931,11 @@ if not preconfigured:
                 color_print(4,'Could not find optional header or shared library for %s' % libinfo[0])
                 env['SKIPPED_DEPS'].append(libinfo[0])            
 
+    if env['ICU_LIB_NAME'] not in env['MISSING_DEPS']:
+        if not conf.icu_at_least_four_two():
+            # expression_string.cpp and map.cpp use fromUTF* function only available in >= ICU 4.2
+            env['MISSING_DEPS'].append(env['ICU_LIB_NAME'])
+    
     if env['THREADING'] == 'multi':
         thread_flag = thread_suffix
     else: