Add a utility command to extract the pertinent parts of a stack trace

  extract-stacktrace.py <dump file>

Will run minidump_stackwalk on the provided dump file and using
a symbol server specified on the command-line and parse the results.
Cache failed symbol lookups

Speed up repeated executions of minidump_stackwalk on dumps which
refer to the same set of system libraries for which symbols are not
available by caching failed lookups for a short period of time.