Just recently in the salesforce sandbox environment, in the REST API login JSON response a new field "is_readonly" is returned that causes our 3rd party code (we are using the Apache Camel Salesforce component) to fail.

The official documentation doesn't mention this "is_readonly" field:
https://developer.salesforce.com/docs/atlas.en-us.api_rest.meta/api_rest/intro_understanding_web_server_oauth_flow.htm

We try to "ant deployUnpackaged" with the Force.com migration tool for standard objects with custom fields, but it seems that some fields were part of the standard fields some releases ago but now they do not appear in a brand new organization. We are getting the following errors:

objects/Account.object (Account.CurrencyIsoCode) -- Error: Could not resolve standard field's name. (line 313, column 13)

The package.xml looks like:
<?xml version="1.0" encoding="UTF-8"?>
<Package xmlns="http://soap.sforce.com/2006/04/metadata">
    <types>
        <members>*</members>
        <name>CustomObject</name>
    </types>
    <version>34.0</version>
</Package>
 

We try to "ant deployUnpackaged" with the Force.com migration tool for standard objects with custom fields, but it seems that some fields were part of the standard fields some releases ago but now they do not appear in a brand new organization. We are getting the following errors:

objects/Account.object (Account.CurrencyIsoCode) -- Error: Could not resolve standard field's name. (line 313, column 13)

The package.xml looks like:
<?xml version="1.0" encoding="UTF-8"?>
<Package xmlns="http://soap.sforce.com/2006/04/metadata">
    <types>
        <members>*</members>
        <name>CustomObject</name>
    </types>
    <version>34.0</version>
</Package>