changes to make nsIFileSpecWithUI useful from javascript.

now, this works from js:

var filePicker = Components.classes["component://netscape/filespecwithui"].createInstance();
filePicker = filePicker.QueryInterface(Components.interfaces.nsIFileSpecWithUI);
file = filePicker.chooseFile("Select a file");

widget/public/nsIFileSpecWithUI.idl

@@ -68,6 +68,7 @@ interface nsIFileSpecWithUI : nsIFileSpec
 	,	in string extraFilterTitle
 	,	in string extraFilter
 		);
+        string chooseFile(in string title);
 	void chooseDirectory(in string title);
 };
 	

widget/src/xpwidgets/nsFileSpecWithUIImpl.cpp

@@ -77,6 +77,14 @@ NS_IMETHODIMP nsFileSpecWithUIImpl::chooseOutputFile(
     return mBaseFileSpec->setFromFileSpec(spec);
 } // nsFileSpecImpl::chooseOutputFile
 
+NS_IMETHODIMP nsFileSpecWithUIImpl::chooseFile(const char *title, char **_retval)
+{
+	nsresult rv = chooseInputFile(title, eAllFiles, nsnull, nsnull);
+	if (NS_FAILED(rv)) return rv;
+	rv = GetURLString(_retval);
+	return rv;
+}
+
 //----------------------------------------------------------------------------------------
 NS_IMETHODIMP nsFileSpecWithUIImpl::chooseInputFile(
 		const char *inTitle,

widget/src/xpwidgets/nsFileSpecWithUIImpl.h

@@ -37,6 +37,8 @@ class nsFileSpecWithUIImpl
 
 	NS_IMETHOD chooseOutputFile(const char *windowTitle, const char *suggestedLeafName);
 
+	NS_IMETHOD chooseFile(const char *title, char **_retval);
+
 	NS_IMETHOD chooseInputFile(
 		const char *title,
 		nsIFileSpecWithUI::StandardFilterMask standardFilterMask,