Bug #10802 --> expose load types to load info class so callers can set the load type

this is needed to implement things like open attachment so we can make the doc shell
think a user click happened when it talks to the uriloader.

I removed two boolean fields which were representing two load types. Simplified the api by allowing you
to pass in any of our load types.
r=valeski

docshell/base/nsDocShellLoadInfo.h

@@ -46,9 +46,8 @@ protected:
 
 protected:
    nsCOMPtr<nsIURI>                 mReferrer;
-   PRBool                           mReplaceSessionHistorySlot;
-   PRBool                           mRefresh;
    nsCOMPtr<nsISupports>            mOwner;
+   nsDocShellInfoLoadType           mLoadType;
    nsCOMPtr<nsISHEntry>             mSHEntry;
 };