Support for whitespace for bootstrap/casper_path

Adding quotations around the file path to allow whitespace in the path
for the bootstrap.js file passed to the execution engine and the
CASPER_PATH argument.
Removing hardcoded Windows path delimiter

Allowing for .NET to determine the OS path delimiter when combining the
path for the bootstrap.js file.
Using 2 arg overload of Path.Combine for .NET 3
Merge pull request #851 from austin-rasmussen/master

Support for whitespace for bootstrap/casper_path