refactor declaration of openchangedb_* functions

Work in progress, this does not compile
adapt emsmdb server to changes on openchangedb_* functions
refactor openchangedb functions to act as proxy calling the real function
openchangedb ldb backend

work in progress, this does not compile yet
initialize function for openchange ldb context
added openchangedb_transaction_* functions
initialization of openchangedb_ldb and fix lots of compilation errors
add missing namedprop_transaction_* functions implementation
Merge pull request #5 from Zentyal/jgarcia/openchange.ldb

Define common interface to access openchange.ldb