SHA2 renamed to SHA256, SHA4 renamed to SHA512 and functions accordingly

The SHA4 name was not clear with regards to the new SHA-3 standard. So
SHA2 and SHA4 have been renamed to better represent what they are:
SHA256 and SHA512 modules.
diff --git a/scripts/generate_errors.pl b/scripts/generate_errors.pl
index 945ab6a..009107b 100755
--- a/scripts/generate_errors.pl
+++ b/scripts/generate_errors.pl
@@ -11,7 +11,7 @@
 my @low_level_modules = ( "AES", "ASN1", "BLOWFISH", "CAMELLIA", "BIGNUM",
                           "BASE64", "XTEA", "PBKDF2", "OID",
                           "PADLOCK", "DES", "NET", "CTR_DRBG", "ENTROPY",
-                          "MD2", "MD4", "MD5", "SHA1", "SHA2", "SHA4", "GCM" );
+                          "MD2", "MD4", "MD5", "SHA1", "SHA256", "SHA512", "GCM" );
 my @high_level_modules = ( "PEM", "X509", "DHM", "RSA", "ECP", "MD", "CIPHER", "SSL",
                            "PKCS12", "PKCS5" );