Fix round decimals with some non English locale

[sgomez]

Decimals in SVG and EPS use the point notation. But in enviroments with intl module activate, the decimals can be represented with commas. For example when we use Spanish or Frech locale numeric.

I propose you to change round with number_format. This function does round too, uses point to decimal notation and returns a string.

[DASPRiD]

This has nothing to do with the intl extension, but when you change the PHP locale to something else. This is simply not supported (changing the locale of the PHP process is a bad idea in general).

[tscheepers]

@DASPRiD Currently the SVG generation code breaks, for all locales that use a comma instead of a dot for the decimal separator, e.g. mainland Europe locales. Dynamically setting it would be a bad idea, but supporting different locales from en_US would be nice right? This PR actually makes sense to me.

[wyattoday]

I agree. This pull request should be accepted.

[DASPRiD]

Well, I'm inclined to allow it, but you'd it needs to strip of redundant trailing zeroes, which this pull request right now wouldn't. It might make more sense to keep the rounding in place and use sprintf() around it instead with the %F formatting, which is non-locale aware.