 Fixing HTTPMultipartUpload.
 Fixing HTTPMultipartUpload.

 The ending boundary for multipart must replace the last boundary, not added
after it.
Review URL: https://breakpad.appspot.com/390002

git-svn-id: a14e546401035be51a469fbea25ecce70a1a22f2@965 4c0a9323-5329-0410-9bdc-e9ce6186880e

tomgr/google-breakpad,tomgr/google-breakpad,tomgr/google-breakpad,tomgr/google-breakpad,tomgr/google-breakpad