* CookieContainer.cs: Provide meaningful information in exception

* CookieContainer.cs: Provide meaningful information in exception
messages, and improve compatibility with MS. Modified set_Capacity to
no longer change MaxCookieSize when new value is less than
MaxCookieSize.
* CookieTest.cs: Added test for Path.
* CookieContainerTest.cs: Added and improved .ctor tests.
Improved tests for Capacity and MaxCookieSize. Added tests for
PerDomainCapacity. Added tests for Add overloads, GetCookieHeader,
GetCookies and SetCookies. Added test for bug #421827.

svn path=/trunk/mcs/; revision=134295