move update code for postcode and word count to Python

Adds also tests for the new function to execute a SQL script.

nominatim/tools/refresh.py

@@ -0,0 +1,16 @@
+"""
+Functions for bringing auxiliary data in the database up-to-date.
+"""
+from ..db.utils import execute_file
+
+def update_postcodes(conn, datadir):
+    """ Recalculate postcode centroids and add, remove and update entries in the
+        location_postcode table. `conn` is an opne connection to the database.
+    """
+    execute_file(conn, datadir / 'sql' / 'update-postcodes.sql')
+
+
+def recompute_word_counts(conn, datadir):
+    """ Compute the frequency of full-word search terms.
+    """
+    execute_file(conn, datadir / 'sql' / 'words_from_search_name.sql')