Provide BigInteger alternative

[GoogleCodeExporter]

As noted in issue 21, GWT compiles a non-performant BigInteger 
(https://code.google.com/p/google-web-toolkit/issues/detail?id=8310). This 
results in RSA key generation taking hours or days when running in production 
mode.

Without waiting for GWT core to fix this, one potential way forward would be to 
wrap jsbn.js (http://www-cs-students.stanford.edu/~tjw/jsbn/) with a JSNI 
BigInteger, and use that instead in the RSA algorithms. 

Original issue reported on code.google.com by quickte...@gmail.com on 5 Feb 2014 at 12:58

[GoogleCodeExporter]

(For reference, Forge, which uses jsbn.js, can create 2048 bit RSA keypairs in 
a minute or two.)

Original comment by quickte...@gmail.com on 5 Feb 2014 at 12:59