(SERVER-211) Update JRuby to 1.7.17 and fix String::crypt

Versions of JRuby prior to 1.7.17 used an old, DES-only implementation
of String::crypt. With 1.7.17, it switched to the native crypt(3)
implementation, bringing it in line with MRI.
Merge pull request #330 from elyscape/SERVER-211-fix-crypt

(SERVER-211) Update JRuby to 1.7.17 and fix String::crypt