freerdp: Use absolute path when calling dlopen

pkgs/applications/networking/remote/freerdp/dlopen-absolute-paths.diff

···
+*** FreeRDP-1.2.0-beta1+android7-src/winpr/libwinpr/smartcard/smartcard_pcsc.c.orig	2015-01-25 19:10:03.971628580 -0800
+--- FreeRDP-1.2.0-beta1+android7-src/winpr/libwinpr/smartcard/smartcard_pcsc.c	2015-01-25 19:55:05.453980544 -0800
+***************
+*** 2807,2816 ****
+  #ifdef __MACOSX__
+  	g_PCSCModule = LoadLibraryA("/System/Library/Frameworks/PCSC.framework/PCSC");
+  #else
+! 	g_PCSCModule = LoadLibraryA("libpcsclite.so.1");
+  
+  	if (!g_PCSCModule)
+! 		g_PCSCModule = LoadLibraryA("libpcsclite.so");
+  #endif
+  
+  	if (!g_PCSCModule)
+--- 2807,2816 ----
+  #ifdef __MACOSX__
+  	g_PCSCModule = LoadLibraryA("/System/Library/Frameworks/PCSC.framework/PCSC");
+  #else
+! 	g_PCSCModule = LoadLibraryA("@pcsclite@/lib/libpcsclite.so.1");
+  
+  	if (!g_PCSCModule)
+! 		g_PCSCModule = LoadLibraryA("@pcsclite@/lib/libpcsclite.so");
+  #endif
+  
+  	if (!g_PCSCModule)

pkgs/applications/networking/remote/freerdp/unstable.nix

···
 { stdenv, fetchFromGitHub, cmake, pkgconfig, openssl, zlib, libX11, libXcursor
 , libXdamage, libXext, glib, alsaLib, ffmpeg, libxkbfile, libXinerama, libXv
+, substituteAll
 , pulseaudio ? null, cups ? null, pcsclite ? null
 }:
 
···
     rev = "1.2.0-beta1+android7";
     sha256 = "08nn18jydblrif1qs92pakzd3ww7inr0i378ssn1bjp09lm1bkk0";
   };
+
+  patches = [
+  ] ++ stdenv.lib.optional (pcsclite != null)
+      (substituteAll {
+        src = ./dlopen-absolute-paths.diff;
+        inherit pcsclite;
+      });
 
   buildInputs = [
     cmake pkgconfig openssl zlib libX11 libXcursor libXdamage libXext glib