Constructor to create UriBuilder from an HttpServletRequest (issue217074)

[johnfargo]

Reviewers: shindig.remailer_gmail.com,

Description:
I believe this works fine but could use some insight into whether I'm
missing edge cases.
Please review this at http://codereview.appspot.com/217074/show

Affected files:
  java/common/src/main/java/org/apache/shindig/common/uri/UriBuilder.java
   
java/common/src/test/java/org/apache/shindig/common/uri/UriBuilderTest.java