misc style issues

7zip.inc : $stream is really a private property.

userDupes.inc : still only used by MysqlUpdater, added a comment about
it and made the properties private.

sql.php : make sure we actually do nothing in some method. Previously we
just had an empty IF statement.

purgeList : a private method was named the same as the class, that is
how we declared constructor with PHP4. Renamed it to doPurge() to make
it clear that it is not the constructor.

Rests are whitespaces fixes.

Change-Id: I0b83f83ee3af37c770817ebfce3e804082c2fb41
Merge "misc style issues"