Fix for pageant-dirhandle': a new wrapper functions request_file()' maintains

a separate CWD for the file requester, so that when the Open File box is not
open Pageant should stay where it was started.
(Also some other minor cleanups in this area of Pageant.)

[originally from svn r5413]
[this svn revision also touched putty-wishlist]

windows/winstuff.h

@@ -173,6 +173,10 @@ struct ctlpos {
 /*
  * Exports from winutils.c.
  */
+typedef struct filereq_tag filereq; /* cwd for file requester */
+BOOL request_file(filereq *state, OPENFILENAME *of, int preserve, int save);
+filereq *filereq_new(void);
+void filereq_free(filereq *state);
 void split_into_argv(char *, int *, char ***, char ***);
 
 /*