Change search populate base task (#1615)

[anvit]

Update search:populate base to arBaseTask instead of sfBaseTask.

[mcantelon]

Thanks for making this, Anvit! There seems to be a weird issue, though, that's a bit of a rabbit hole. The search engine sends log messages through the log method in lib/search/QubitSearchEngine.class.php and, for some reason, when the base class of the search populate task is changed this ends up (when I run it) making log messages not show in the console display.

[anvit]

Closing for now, will reopen when we decide to revisit this.