Unicorn 1.0.1 and 1.1.2 - fix rollbacks

Changes:

Theses release fix a long-standing bug where the original PID
file is not restored when rolling back from a USR2 upgrade.
Presumably most upgrades aren’t rolled back, so it took over a
year to notice this issue. Thanks to Lawrence P. for
discovering and reporting this issue.

About Unicorn:

Unicorn is an HTTP server for Rack applications designed to only serve
fast clients on low-latency, high-bandwidth connections and take
advantage of features in Unix/Unix-like kernels. Slow clients should
only be served by placing a reverse proxy capable of fully buffering
both the the request and response in between Unicorn and slow clients.