MinGW needs an extra symbol _WIN32_IE defined to a particular value before

it'll let you see an identifier (SHGFP_TYPE_CURRENT) referenced since r7082.
(Actually, you need a pretty recent w32api before it's there at all.)

Morally, this should be defined for all toolchains, not just MinGW/Cygwin, but  I'll leave that to people who have those toolchains.
<http://msdn2.microsoft.com/en-us/library/aa383745.aspx>

Also add some other comments on our use of this API (since it's a horrible one
that I suspect will come back and haunt us...)

[originally from svn r7087]
[r7082 == dbbd6eb5ec]
[this svn revision also touched putty-wishlist]

windows/winstore.c

@@ -492,6 +492,12 @@ static HANDLE access_random_seed(int action)
      * versions of Windows.
      */
     if (!tried_shgetfolderpath) {
+	/* This is likely only to bear fruit on systems with IE5+
+	 * installed, or WinMe/2K+. There is some faffing with
+	 * SHFOLDER.DLL we could do to try to find an equivalent
+	 * on older versions of Windows if we cared enough.
+	 * However, the invocation below requires IE5+ anyway,
+	 * so stuff that. */
 	shell32_module = LoadLibrary("SHELL32.DLL");
 	if (shell32_module) {
 	    p_SHGetFolderPath = (p_SHGetFolderPath_t)