Properly support JAR manifest line continuations

Fix for bugzilla 841569.
Additional fixes for continuation parsing

- Alpha order the imports
- Add two newlines when parsing since it won't hurt anything to match the
  comments
- Reset the loop iteration persistent header variable when we start a new
  parsing a new section just to be safe
- Still bugzilla 841569
Add additional tests

To make me feel warm and fuzzy
Merge pull request #5 from mozilla/line-continuation-support

Properly support JAR manifest line continuations