Bug 1027131 - Split out ExportHelpers.cpp. r=gabor

A lot of this stuff is usable from both Sandbox.cpp and XPCComponents.cpp, and
those files are both pretty big these days.
Bug 1027131 - Remove invalid assertion. r=gabor

If a clone happens between two same-origin scopes, we'll end up with CCWs here
that are neither Xrays nor reflectors.
Bug 1027131 - Rename CloneNonReflectors into StackScopedClone, and give it an options struct. r=gabor
Bug 1027131 - Switch to a struct for the StackScopedClone closure. r=gabor
Bug 1027131 - Add support for Blob and FileList in the wrapReflectors = false case. r=gabor
Bug 1027131 - Innerize before reflector detection. r=gabor
Bug 1027131 - Add support for function cloning in StackScopedClone. r=gabor
Bug 1027131 - Use StackScopedClone for cloneInto. r=gabor
Bug 1027131 - Additional tests for wrapReflectors. r=gabor