* FileWebRequest.cs: Fixed PreAuthenticate and Proxy properties to

* FileWebRequest.cs: Fixed PreAuthenticate and Proxy properties to
no longer throw NotSupportedException. No longer store ContentLength
in headers. Do not allow null or zero-length method. Allow timeout
to be set to -1 (infine). Only disallow GET, HEAD and CONNECT requests.
Removed workarounds for bug #24943. In (Begin)GetRequest overwrite
file if it already exists. Binary serialization compatibility fixes.
* FileWebResponse.cs: Return application/octet-stream as ContentType.
* FileWebRequestTest.cs: Reworked tests to no longer rely on TMPDIR.
Added tests for ConnectionGroupName, ContentLength, ContentType,
Credentials, GetRequestStream, GetResponse, Method, PreAuthenticate,
Proxy, RequestUri, Timeout. Added binary serialization compatibility
tests.
* FileWebResponseTest.cs: Added tests for ContentLength, ContentType,
GetResponseStream, Headers, ResponseUri.
* System_test.dll.sources: Added FileWebResponseTest.cs.

svn path=/trunk/mcs/; revision=71809