Symbolication tweaks

After this change KSCrash is capable of generating reports that
can pass all of the CrashProbe tests. To do this I had to:

- Include the link register in the backtrace on arm.
- Detag instructions more conservatively.
- Treat addresses from stack walking as return addresses.
Merge pull request #77 from ConradIrwin/more-precise-symbolication

Symbolication tweaks