Support unmodified Xpdf binaries

Use stdout redirection scripts for pdfinfo and, on Windows, a script to
run pdftotext hidden, which together allow for all unmodified binaries
(including, probably, symlinked system ones, though I didn't test that).

On Windows, using a .vbs does cause a brief wait cursor. The stock
pdfinfo needs the redirection script anyway, so that's unavoidable, but
on the async branch I think we'll be able to switch to pdf.js for the
page count, at which point maybe I'll try to remember how I modified the
Windows binaries to be hidden and use a modified version of pdftotext to
avoid VBScript. (We use the stock pdftotext elsewhere already.)

resource/hide.vbs

@@ -0,0 +1,24 @@
+Option Explicit
+
+Dim WshShell, fso, exe, args, I
+
+Set WshShell = Wscript.CreateObject("Wscript.Shell")
+Set fso = WScript.CreateObject("Scripting.FileSystemObject")
+
+If WScript.Arguments.Count = 0 Then
+  WScript.Echo "Usage: hidden.vbs program.exe [args...]"
+  WScript.Quit 1
+End If
+
+exe = WScript.Arguments(0)
+If Not(fso.FileExists(exe)) Then
+  WScript.Echo "Executable not found: " & exe
+  WScript.Quit 1
+End If
+
+args = ""
+For I = 1 to WScript.Arguments.Count - 1
+  args = args & " " & chr(34) & WScript.Arguments(I) & chr(34)
+Next
+
+WshShell.Run exe & args, 0, true