OpenSSL library updated to 1.0.1h

Previous versions of the library contain a vulnerability CVE-2014-0224.
Merge pull request #581 from deg84/openssl_101h_update

OpenSSL library updated to 1.0.1h
Fix `fetch_git` with `--keep`

Update existing git repo if exists, or clone if not exists.
The destination repo might exist if the `--keep` was supplied for `ruby-build`.
Add tests for `fetch_git`
Surely update local git working copy