bugfixing, documentation in global/debug

- catch missing "controlDict" file immediately via findEtcFile() instead of
  checking IFstream::good(). This avoids segfaulting, since the error
  handling in IFstream uses classes that are not yet initialized.
- use new dictionary features (eg, lookupOrAddDefault) to reduce code
- fixed debug::switchSet to use ref-to-pointer so pointer actually gets set!