Indexer: add getPID/getPageFromPID functions and PID to INDEXER_PAGE_ADD

This allows plugins to get the PID for a page and also to get the page
for a certain PID. That way plugins can build their own index that uses
numeric ids.
Indexer: Add test case for the PID functions
Indexer: Add cache for getPID()

This avoids re-reading of the page index file for every getPID()-call by
using a simple FIFO cache, limited to 10 items. In idx_addPage() and the
functions that it calls getPID() is called 3 times for the same PID.
Indexer: Make $Indexer in idx_get_indexer() global instead of static

This avoids problems with test cases that use the indexer and the PID
cache - the index is cleaned between test cases but the PID cache
wasn't cleaned. Now PHPUnit can unset the global $Indexer between test
cases.
Add clear function to the indexer that deletes the whole index
Remove global $Indexer, clear index in the testing system instead
Remove superfluous requires and variables from bin/indexer.php
Made auth_aclcheck always return int

The returned type is important in particular when we deal with xmlrpc. Indeed,
this value is directly returned to the client eg when the wiki.getAllPages method
is queried.

Currently the 'perms' attribute may be either an int or a string, and its up to
the xmlrpc client to resolve it (although Dokuwiki's documentation only tells it
can be an int).

This patch makes sure we'll always return perms as int.
Merge pull request #151 from gturri/master

xmlrpc putPage and appendPage should return bool
Arabic language update
Merge pull request #153 from gturri/xmlrpcPerms

Made auth_aclcheck always return int
Merge pull request #148 from michitux/indexer

Indexer: Add the PID to INDEXER_PAGE_ADD and add getPID/getPageFromPID functions
allow template unit tests
Traditional Chinese language update
show filesize of local file links in tooltip