tests: add scrypt_tests.cpp to verify sse2

[vertiond]

49f9594 fixes the --enable-sse2 flag but without a test case we can't be sure that sse2 is indeed working.

We should look into porting a test case such as https://github.com/litecoin-project/litecoin/blob/master/src/test/scrypt_tests.cpp

[vertiond]

scrypt-sse2 removed from future releases until a test case is made