- Refresh do-not-use-sphinx.diff

- update to 1.4.20:
* Enable -fvisibility-inlines-hidden option if the compiler supports it.
* Add missing reference tracking. XapianEnquire now keeps a reference to the
current XapianSorter object (if any). XapianQueryParser now keeps a
reference to any set XapianFieldProcessor objects. Test coverage for keeping
references to set functor objects is now more comprehensive.
* smoketest.php: Remove bogus extra null parameters. PHP ignores these extra
parameters, but it's more helpful to be testing valid usage.
* The configure probes for Python3 no longer use the deprecated distutils and
imp modules (both of which are slated for removal in Python 3.12). We now
use sysconfig to get the directory to install the xapian module to, which may
result in it being installed in a different place (it should still work, but
if you're packaging the bindings you may need to update the list of files to
include in the package). (forwarded request 990268 from bnavigator)