[SCons] Check for <tr1/tuple>

This header is used by GTest. If not present, define 'GTEST_USE_OWN_TR1_TUPLE'
to use an alternative version. Fixes a compilation error on OS X.

test/SConscript

@@ -9,6 +9,9 @@ localenv.Prepend(CPPPATH=['#ext/gtest/include', '#include'],
 localenv.Append(LIBS=['gtest'] + localenv['cantera_libs'],
                 CCFLAGS=env['warning_flags'])
 
+if not localenv['HAS_TR1_TUPLE']:
+    localenv.Append(CPPDEFINES='GTEST_USE_OWN_TR1_TUPLE')
+
 localenv['ENV']['CANTERA_DATA'] = Dir('#build/data').abspath
 
 PASSED_FILES = {}