make TikaMW file access compatible with MediaWiki 1.21

MediaWiki changed their API for getting stored files.  As of
5275f9b097cdae5dbab0845e3ea127086e3a6570 on mediawiki/core,
File::getPath() no longer returns a path on the physical
file system.  Instead, it uses mwstore:// paths, which when
passed to PHP functions like file_exists() and file_get_contents(),
causes warnings.  The fix is to use File::getLocalRefPath()
instead.  This can be verified in this diff:

https://git.wikimedia.org/commitdiff/mediawiki%2Fcore/5275f9b097cdae5dbab0845e3ea127086e3a6570

wherein one can see the old API calls getting replaced
with the new API.
make file path resolution fix more robust

This commit is based on feedback from vitalif on my pull request

https://github.com/mediawiki4intranet/TikaMW/pull/1#issuecomment-24405255

The change involves a static variable that stores the method name
to be used in getting a file system path.  It is computed once
upon first invocation, where we attempt to figure out whether
the File object support the newer API.
Remove some spaces, move title check re-enabling to the correct place