mapistore/oxio: Implement Indexing using Opechange MySQL database

Hence, _Index class completely refactored into now _Indexing
 * use MySQL mapistore_indexing for Get/Add new URLs
 * use mapistore_indexes to allocate new Index number
   + a conversion into Exchange FMID
 * transparent conertions between Index format for URIs and
   OXIO format of URI

todo:
 * Username should be propagated to the index
 * may be reractor this code as a thin wrapper on top of future
   python bindings for Indexing service
Add PyBool/boolean support to python mapistore property mapping
Add PidTagSubfolders and set it to False for child folder of sample backend
Merge branch 'jkerihuel/mapistore-python' of https://github.com/openchange/openchange into jkerihuel/mapistore-python
Add required set of properties to the message so that it can be displayed in Outlook 2010
Move the message underneath deadbeef rather than dead1001
Add cache in dictionary when creating new folder
Add support for PT_I8
Merge branch 'jkerihuel/mapistore-python' of https://github.com/openchange/openchange into jkerihuel/mapistore-python
mapistore/oxio: Dump uri passed in Context constructor
HACK: mapistore/python: preload libpython2.7 with RTLD_GLOBAL

This is for sesequent modules loading to work
HACK: Skip provisioning every time mailbox is opened
HACK: Makefile: don't install python backends - i'm using symbolic link
WIP: mapipstore_backend: Gather as much context as we can - don't fail if backend fail

oxio for instance doesn't support this call yet
HACK: oxio.py: Prefix folder names with 'OXIO-' so it is visble when it come from