[AC-1906] md5 checksum for blobs on Android broken

The implementation of md5 checksum for Android is broken for binary blobs. In https://github.com/appcelerator/titanium_mobile/blob/master/android/modules/utils/src/java/ti/modules/titanium/utils/UtilsModule.java the method public String md5HexDigest(Object obj) { String data = convertToString(obj); if (data != null) { return DigestUtils.md5Hex(data); } return null; } is incorrect since converting a blob to a string before computing md5 on it gives incorrect md5 checksums. The correct implementation should be public String md5HexDigest(Object obj) { if (obj instanceof String) { return DigestUtils.md5Hex((String)obj); } else if (obj instanceof TiBlob) { return DigestUtils.md5Hex(((TiBlob) obj).getBytes()); } return null; }