delete old files that have been replaced by a directory

Fixes #417.
Replaces #1086, more logical code.
test this fix with a cucumber feature
Catch conversion errors. Constituent of #1105.
Merge pull request #1253 from mojombo/catch-conversion-errors

Catch conversion errors.
Update history to reflect merge of #1253
Merge pull request #1118 from maul-esel/dir-bug-take2

[bugfix #417] delete old files that have been replaced by a directory
Update history to reflect merge of #1118
Update template for Travis message in #jekyll irc room.