Limit search results from DB; fix #7049

This caps the search results at 1000 emails, due to our unfortunate
requirement of constructing an object for each search result.  A better
way to proceed here would be to do the search only as items were loaded
in the SearchFolder, but that gets complicated when the search phrase
gets updated.

sql/version-011.sql

@@ -0,0 +1,7 @@
+--
+-- Add the internaldate column as a time_t value so we can sort on it.
+--
+
+ALTER TABLE MessageTable ADD COLUMN internaldate_time_t INTEGER;
+
+CREATE INDEX MessageTableInternalDateTimeTIndex ON MessageTable(internaldate_time_t);