Fix ignored paths regression in prr-apply dirty check

[danobi]

0889e77 regressed dirty checks. I think we want to bring back status_opts.include_ignored(false);.

Regression (with some debug info):

$ git status
On branch master
Your branch is up to date with 'origin/master'.

nothing to commit, working tree clean
$ ./target/debug/prr apply 47
".prr.toml": Status(IGNORED)
".prr/": Status(IGNORED)
".tags": Status(IGNORED)
"target/": Status(IGNORED)
Error: Working directory is dirty

Fix should come with a unit test. We can use libgit2 to init a repo in a temp dir

[danobi]

Looks like we also need to strip out PR description if it exists. If there were tests for prr-apply we probably wouldn't have regressed :p