[cairo] miter limits less than one

[Adrian Johnson]

Behdad Esfahbod wrote:
> Cause error in PS

The PS Language Reference requires the PS miter to be >= 1.

> (and PDF I guess).

The PDF Reference does not specify miter limits however acroread fails
to display pages when the miter is < 1. Older versions of ghostscript
crash when the PDF miter is < 1.

I've pushed out a fix for PS/PDF to ensure the emitted miter is
always >= 1.