Implementing surprisingness evaluation - half way.
Finished surprisingness evaluation.
Removed normalization for surprisingness.
Added variable number to pattern.
Consider the variable number of a pattern, when two patterns have same surprisingness value, the pattern has less variables ranks higher.
Merge pull request #1022 from shujingke/PM

Surprisingness evaluation for interesting pattern mining.
Guile unit test: put the sequence of tests into order.
atomspace: fix broken operator<<()
scheme: Fix output port drain
Guile: provide documentation for the new code.
Merge pull request #1024 from linas/bugfix

Bugfix for #1023