Floating point comparisons

The exact value of a floating point value may vary depending on the order of the operands, the machine precision, the implementation of standard numerical functions, etc. For these reasons it is seldom meaningful to compare two floating point values to determine if their values are exactly equal. To circumvent this problem we introduce a user specified value tex2html_wrap_inline309 which is the largest tolerated difference when comparing two floating point values before an error is reported.