GUI: Find dialog: Compare only to the decimal places of the print format.

When using the find dialog of the data editor, previously a numeric value
was compared exactly on it's underlying representation (a IEEE754 double
precision float).   This is problematic, because most such floats cannot
be precisely represented in a decimal format, and even if they can be, the
precision required might well exceed that displayed in the data editor.

This change rounds both the reference and the comparand to the number of
decimal places indicated by the variable's print format.