Add missing MD_MISCINFO_FLAGS1_BUILDSTRING. Revise documentation to clarify
that it is not enough to check the size of an MDRawMiscInfo stream to verify
member validity, the flags1 field needs to be consulted as well. Update
minidump_dump to correctly consider the validity of all fields in this
structure.

R=ivanpe@chromium.org

Review URL: https://breakpad.appspot.com/3694002

git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@1336 4c0a9323-5329-0410-9bdc-e9ce6186880e