Fixed SecureRandom PRNG problem.

Solution copied from
http://android-developers.blogspot.de/2013/08/some-securerandom-thoughts.html
Sometimes /dev/urandom is not writable.

Copied again from http://android-developers.blogspot.de/2013/08/some-securerandom-thoughts.html
Check B % N != 0 in SRP algorithm.
Removed an spurious comment.
Add package declaration and attribution source to PRNGFixes.java
Merge branch 'bug/secure-random-vulnerability' into develop
Merge branch 'bug/srp-b-validation' into develop