General improvements:

- There might be special cases that require the unique key to be a string
  (just ran into one); since this is not a generally useful change, it's
  hidden behind #defines.
- Added essential support for telephoneNumber match; the same infrastructure
  might be useful for other specialized matches (also regular matches should
  use it to handle multiple spaces and so!).
- Fixed dynamic backend initialization.
- Cleaned up search base DN normalization (works also if no uppercase function
  is available, using case exact matches).