"ServletScopes.REQUEST already bound" when ServletModule used with Modules.override or PrivateModule

_From [jeffjcrowe](https://code.google.com/u/116966542706070883618/) on July 04, 2011 21:02:01_

When ServletModules are combined with PrivateModule or Modules.override (for test code), Injector creation fails with the binding errors below.

Code to reproduce:

Guice.createInjector(new AbstractModule(){
  `@`Override
  protected void configure() {
    install(new ServletModule ());
    install(new PrivateModule() {
      `@`Override protected void configure() {
        install(new ServletModule ());
      }
    });
  }
});

OR

Guice.createInjector(new AbstractModule(){
  `@`Override
  protected void configure() {
    install(new ServletModule ());
    install(Modules.override(new ServletModule ()).with());
  }
});

1) Scope ServletScopes.REQUEST is already bound to com.google.inject.servlet.RequestScoped. Cannot bind ServletScopes.REQUEST.
  at com.google.inject.servlet.InternalServletModule.configure(InternalServletModule.java:77)

2) Scope ServletScopes.SESSION is already bound to com.google.inject.servlet.SessionScoped. Cannot bind ServletScopes.SESSION.
  at com.google.inject.servlet.InternalServletModule.configure(InternalServletModule.java:78)

3) A binding to javax.servlet.ServletRequest was already configured at com.google.inject.servlet.InternalServletModule.configure(InternalServletModule.java:79).
  at com.google.inject.servlet.InternalServletModule.configure(InternalServletModule.java:79)

... output snipped ..

_Original issue: http://code.google.com/p/google-guice/issues/detail?id=639_

Start with the reproduced injector configurations in the issue and read com.google.inject.servlet.InternalServletModule.configure, especially the lines reported in the binding errors. Determine why installing ServletModule through PrivateModule or Modules.override repeats the request and session scope bindings. Done means both reproductions create an injector without the duplicate-binding errors.

Written by the indexing model from the issue text.