Allow setting a limit on the number of frames to be recovered by stack scanning.
Patch by Julian Seward <jseward@acm.org> R=ted at https://bugzilla.mozilla.org/show_bug.cgi?id=894264

git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@1206 4c0a9323-5329-0410-9bdc-e9ce6186880e