detect tandem repeats with count 2

Currently, the tandem repeat finder allows only a minimal repeat count of x3. That makes sense for short repeats such as mini- or micro-satellites but not for long tandem repeats.

The attached sequence contains a two-copy tandem repeat with a period size of 226 starting at position 110. It is not detected by the repeat finder.

Proposal: allow a minimal repeat count of x2 (maybe starting from a certain length), but keep the default to x3.