Create temp files in the temp directory

Fixes #228

src/GitHub.Api/IO/NiceIO.cs

@@ -697,6 +697,18 @@ GitHub.Unity
             }
         }
 
+        public static NPath GetTempFilename(string myprefix = "")
+        {
+            var random = new Random();
+            var prefix = FileSystem.GetTempPath() + "/" + (String.IsNullOrEmpty(myprefix) ? "" : myprefix + "_");
+            while (true)
+            {
+                var candidate = new NPath(prefix + random.Next());
+                if (!candidate.Exists())
+                    return candidate;
+            }
+        }
+
         public NPath Move(string dest)
         {
             return Move(new NPath(dest));

src/GitHub.Api/OutputProcessors/ProcessManager.cs

@@ -76,7 +76,8 @@ namespace GitHub.Unity
             {
                 // we need to create a temp bash script to set up the environment properly, because
                 // osx terminal app doesn't inherit the PATH env var and there's no way to pass it in
-                var envVarFile = environment.FileSystem.GetRandomFileName();
+
+                var envVarFile = NPath.GetTempFilename();
                 environment.FileSystem.WriteAllLines(envVarFile, new string[] { "cd $GHU_WORKINGDIR", "PATH=$GHU_FULLPATH:$PATH /bin/bash" });
                 Mono.Unix.Native.Syscall.chmod(envVarFile, (Mono.Unix.Native.FilePermissions)493); // -rwxr-xr-x mode (0755)
                 startInfo.FileName = "open";