Add utility to generate backtraces from core files

This should help with getting people reporting issues to provide us
the exact and complete debugging information we need.  In many cases
we'll be able to have them just run this script against their core
file.
Refactor to use gdb printf
Add symbols for version information

This allows us to automatically pull the version of FS out of a core
file for better reporting of bugs.
Log FS version with backtrace-from-core