add the install target, it is missing from the shipped source

--- a/SConstruct
+++ b/SConstruct
@@ -664,6 +664,7 @@
   result = Options()
   result.Add('mode', 'compilation mode (debug, release)', 'release')
   result.Add('sample', 'build sample (shell, process)', '')
+  result.Add('install', 'install result files', '')
   result.Add('env', 'override environment settings (NAME0:value0,NAME1:value1,...)', '')
   result.Add('importenv', 'import environment settings (NAME0,NAME1,...)', '')
   for (name, option) in SIMPLE_OPTIONS.iteritems():
@@ -989,12 +990,33 @@
   env.Alias('sample', samples)
   env.Alias('d8', d8s)
 
+  install_dirs = []
+  destdir = ARGUMENTS.get('DESTDIR', '')
+  prefix = ARGUMENTS.get('PREFIX', '/usr')
+  libdir = [ destdir + prefix + '/lib/' ]
+  incdir = [ destdir + prefix + '/include/' ]
+  for lib in libraries:
+    env.Install(libdir, lib[0])
+    if dir not in install_dirs:
+      install_dirs += libdir
+  for include in [ 'include/v8.h', 'include/v8-debug.h' ]:
+    env.Install(incdir, include);
+  install_dirs += incdir
+  env.Alias('install', install_dirs)
+
+  # Always build at least the library
+  env.Default('library')
+
+
   if env['sample']:
     env.Default('sample')
+  elif env['install']:
+    env.Default('install')
   else:
     env.Default('library')
 
 
+
 # We disable deprecation warnings because we need to be able to use
 # env.Copy without getting warnings for compatibility with older
 # version of scons.  Also, there's a bug in some revisions that