Replacing binlog_row_based_if_mixed with variable binlog_stmt_flags
holding several flags and adding member functions to manipulate the
flags.

Added code to generate a warning when an attempt to log an unsafe
statement to the binary log was made. The warning is both pushed to the
SHOW WARNINGS table and written to the error log. The prevent flooding
the error log, the warning is just written to the error log once per
open session.