Munge the coding line instead of removing it

We want to keep line numbers the same, but Python complains if we have a
coding line in a unicode that we try to exec. Includes tests.
Failing test for bug in coding handling

We need to take the first coding if two coding lines are given.
Fix bug in handling of two coding lines
Merge pull request #332 from gittip/fix-coding-bug

Fix coding bug