tol argument in zero_range is too strict

[richierocks]

The default argument to zero_range's tol argument is currently .Machine$double.eps * 100, or about 2.2e-14. This can cause ggplot to incorrectly warn about bars not being the same width.

See , e.g.,

http://stackoverflow.com/questions/14476961/why-do-i-get-position-dodge-requires-constant-width-even-though-widths-are-con

[hadley]

Not actually sure what it should be, but this seems like a common tolerance.