Fix strange issue on iOS 7 where a simple regular expression appears to cause a complete browser crash.

Closes #306.
Include latest version of straps that solves an issue with injecting DomElement into PaperScope.
Implement support for Hi-DPI canvas on Retina screens.
Optimise DomElement.getPrefixValue()
Include latest version of straps.js
Allow the minification of the undefined variable by defining it as a local parameter inside the paper scope.
Minor improvement in Base.equals()
Replace typeof x !== 'undefined' checks with typeof x === 'object'.
Switch from options.browser and options.node to options.environment
No need for default parameter.
Clean up SVGExport node example.
Adapt to new bower_components directory.
Fix regression issues with Curve-Line intersection code
Calculate correct parameter for linear segments
Override default isEmpty method for Shape

Fixes (new Group([new Shape.Rectangle(...)])).bounds throwing ReferenceError when using Item's isEmpty
Merge pull request #308 from ojj11/isEmptyFix

Override default isEmpty method for Shape
Remove doc comment since Item#isEmpty() is already documented, and move it to an inline comment.
Move Shape#isEmpty() to right place.
Clean up throw statements.

Never throw plain strings.
Improve CanvasView constructor.

Support canvas / size arguments, but not both together, and throw exception if both fail.