Added MarkupExtension tests for testing strings with spaces and commas as parameter (commonly used in file paths), where some tests are currently failing.
Fixed so that MarkupExtensionParser doesent ignore escaped backslash
Fixed bug that double escaped backslashes became three backslashes after parsing
Merge pull request #478 from gumme/WpfDesignerMarkupExtensionParserFix

Wpf designer markup extension parser fix