more tests to improve code coverage

Merge branch 'master' into fread3006

Improves diagnostic messaging of .SDcols when passed bad data (#3117)

more coverage

tidy; e.g. we have modern wide screens, no need to expand vertically. Many times I don't look at the detail of long error messages and I like them to be over on the right off the screen. If I need to look at the detail I scroll over. Expanding statements vertically gets in the way of the logic, imo.