Use a table alias for compatibility with other extensions
Use a table alias for compatibility with other extensions

The current solution of just using a 'page_props' table in the
query makes it impossible for other extensions to utilize this
table in the query as well, one will end up with ambiguous field
name errors. I added an alias for the table to alleviate that.

Change-Id: I3cd45f4db479700bc3d413775a9c64d81b10ef36

wikimedia/mediawiki-extensions-Disambiguator,wikimedia/mediawiki-extensions-Disambiguator