add error reporting, skip existing page revisions

Note: may want to change "ERROR empty page" to "Not importing deleted page"
or something less panicky like that
More debug printouts!

We likes printingses, yessss
Handle empty footnotes better

Return an empty string instead of None when a footnote with no argument
exists, like [[Footnote]]

Fixes errors like:

ERROR render_wikitext (page webster comfort care home): sequence item 1: expected string or Unicode, NoneType found

When faced with a revision like:

https://rocwiki.org/Webster_Comfort_Care_Home?action=diff&version2=4&version1=3
Fix warning on start

Fixes:
/usr/lib/pymodules/python2.6/sapling/scripts/syc_import.py:1461: FutureWarning: The behavior of this method will change in future versions. Use specific 'len(elem)' or 'elem is not None' test instead.
Fix extraneous quotes around addresses
possible performance optimization (ha)
Add Flickr macro support

Ugly, but possibly functional
Add some more error handling...
Try to handle more complicated redirects better

We have a number of pages where there's something like
    #redirect Blah Blah
    ## This line will freak things out

This may handle that better.  :-)
Actually process redirects
Spread page import across multiple processes

Retool the flow such that a pool of workers (hard-coded at 4,
the number of CPU cores exposed by Linode) handles processing
of individual elements.

Hunks of XML are passed to these workers using a Queue(), and
these workers pass Redirect requests out through another
Queue(), consumed later on.

Other misc. fixes are also here, in this commit.

Note: This has not yet made it through a full import run yet,
but I'm crossing my fingers!
Format legacy passwords for direct Django import

Addresses LocalWiki issue #94
Use more smart_str to avoid unicode print errors
Decrease printing to less-ridiculous levels
Clear out non-superusers when cleaning db
Preserve join time when transferring users

Also import the password, if it exists
flickr macro handler: cache stuff

The Flickr API gets cranky if we hit it too hard.  So, cache
more vigorously.
Adjust subprocess output to use a queue

This avoids a problem where prints were stepping on each
other, making troubleshooting/debugging tough.
More farting around with import_from_export_file

Deal with hung processes a bit, also make output more
svelte.
Clear out old files as well as the db entries

Keeps the files directory from getting very full on
repeated imports :-)