test: changed the way to embed googletest.

Before googletest was not supported `make install`.
But not anymore.

test/SConstruct

@@ -8,26 +8,10 @@ def path_chomp(path):
         return path[:-1]
     return path
 
-if not 'GTEST_ROOT' in os.environ:
-    print "set environment variable 'GTEST_ROOT'"
-    Exit(1)
-
-gtest_root = path_chomp(os.environ['GTEST_ROOT'])
-if gtest_root[-1] == '/':
-    gtest_root     = gtest_root[:-1]
-
-gtest_includes = gtest_root + '/include'
-gtest_libs     = gtest_root + '/lib/.libs'
-
-flags    = ['-Wall', '-O2']
-libs     = ['stdc++', 'pthread']
-includes = ['..', gtest_includes]
-target   = 'dtl_test'
-
-env  = Environment(CPPFLAGS=flags,
-                   CPPPATH=includes,
-                   LIBPATH=[gtest_libs],
-                   )
+env  = Environment(
+    CPPFLAGS=['-Wall', '-O2'],
+    CPPPATH=['..'],
+)
 
 conf = Configure(env);
 
@@ -35,6 +19,7 @@ if not conf.CheckCXX():
     print "c++ compiler is not installed!"
     Exit(1)
 
+libs = ['stdc++', 'pthread', 'libgtest']
 for lib in libs:
     if not conf.CheckLib(lib):
         print "library " + lib + " not installed!"
@@ -42,12 +27,15 @@ for lib in libs:
 
 conf.Finish()
 
-test = env.Program(target,
-                   [Glob('*.cpp'), gtest_libs + '/libgtest.a']
-                   )
+test = env.Program(
+    'dtl_test',
+    [Glob('*.cpp')],
+)
 
-test_alias = env.Alias('check',
-                       test,
-                       test[0].abspath)
+test_alias = env.Alias(
+    'check',
+    test,
+    test[0].abspath
+)
 
 env.AlwaysBuild(test_alias)