[Fix #800] Do not report [Corrected] if correction wasn't done

A few cops that support auto-correction avoid it in certain cases.
They should only print [Corrected] if a change was made. Solution is
to reintroduce the exception CorrectionNotPossible that was removed
a while back.
Merge pull request #962 from jonas054/fix_800_corrected

[Fix #800] Do not report [Corrected] if correction wasn't done
Expand base dir to avoid exception from Pathname

The bug would appear when using the value of
`Rubocop::ConfigLoader::DOTFILE` as the command line argument for the
`-c` flag.
Merge pull request #968 from bquorning/expand-config-path

Expand base dir to avoid exception from Pathname
Let the Debugger cop also check for byebug calls
Merge pull request #969 from bquorning/byebug-is-a-debugger

Let the Debugger cop also check for byebug calls
Fix typos
`TrivialAccessors` accepts DSL-style writers.