Various parts of code used different 'precision' arguments for sprintf("%g") when converting
floating point numbers to a string. This led to differences in results in some cases 
depending on whether the text-based or prepared statements protocol is used for a query.

Fixed by changing arguments to sprintf("%g") to always be 15 (DBL_DIG) so that results are
consistent regardless of the protocol.

This patch will be null-merged to 6.0 as the problem does not exists there (fixed by the
patch for WL#2934).