Fix segfault
Hacking around feature-selection bugginess
Expand the sparse table test
feature selection should not choke on dates
Make sure that preserved columns work.

Specificallly, the 'date' column in the input file should be copied over
to the output file.
Test multiple column forcing
Fix failure reading csv table headers

Unfortuately, the boost::trim library is incompatible with the
boost::find library, so use std::find instead.
Hush up a compiler warning
Merge pull request #698 from linas/sparse

fix feature selection so that it works again.