Correctly indent concatenation sub regexps.
Introduce new tests.
Introduce new benchmarks for alternations.
Let the FF_finder access the RegexpInfo to allow more complex processing.

Access to the RegexpInfo will be needed to allocate new regexps.
Introduce suffix tree code, that will be used for common substring extraction.

This code uses a very simple implementation of the suffix tree construction. It
should later be improved to use a more efficient (Ukkonen's?) algorithm.
Perform common substring extraction on fast forward elements.