write error message to log file in case insert to file cache failed - took hours to find that the insert failed :-(
enable UTF-8 charset on mssql
disable MDB2_PORTABILITY_EMPTY_TO_NULL for mssql to allow insert of empty string to no null fields
Merge pull request #2254 from owncloud/fixing-mssql-utf8-and-insert-empty-string-master

Fixing mssql utf8 and insert empty string master