SVG parsing test failures with boost 1.59

[springmeyer]

When built against boost 1.59 new SVG test failures appear: https://gist.github.com/springmeyer/dbecaf9ca6a40ebfd04b.

The cause is newly encountered:

Failed to parse double: "105000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
Failed to parse double: "-105000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"

This looks like the same (cause) as reported at mapnik/mapnik#3111

/cc @artemp for advice on how to fix, or whether we should just update the test fixtures to be different.

[wilhelmberg]

Same thing on Windows: #520