To indicate that something went wrong (e.g. the task already was unprioritized).
Note: For actions that handle multiple ITEMs in a loop, we cannot use die() as that would abort processing of any following ITEM(s). Instead, use a status variable and set it to 1 on error, then exit at the end.
Before adding any more features to todo_completion, I feel like I need test coverage, so this is a first stab at testing the completion results, via a new test function test_todo_completion.
Some basic tests showcase the capabilities.
Note: test-lib.sh now uses arrays, therefore all tests must use /bin/bash, not /bin/sh to avoid errors when sourcing test-lib. For consistency with todo.sh, we should have used Bash everywhere, anyway. Also note that t2000-multiline.sh needs some more quoting to avoid "Bash: ambiguous redirect" errors.
The sed command of BSD / OS X doesn't like { command } blocks in a single expression. So move the (dynamic) deduplicate sed command(s) to the end, and use a label to access them. This also makes the entire sed script somewhat easier to understand.
As per discussion on the mailing list (http://tech.groups.yahoo.com/group/todotxt/message/3775), the automatic deduplication during archiving is unexpected and difficult to enforce in other implementations. Rather, make this a separate (optional) action.
