Fix mysql import with a zero value for auto id increment

The id = 0 is used in the 'fournisseur' table to indicate the
'Multiples' fournisseur.
But in mysql an id = 0 for an autoincrement, is interpreted as 'null'
and mysql assign the next available id (instead of zero).
There is a sql mode to consider zero as zero. The fix add the mode at
the right places (when launching mysql server or at run time in case
the server is already running).
HINT: mysqlimport doesn't accept sql mode in command line, so mysqlexport
is replaced by the mysql client version (LOAD DATA INFILE...)