Fix breaking test cases on unix platform

Rename platform parameter file to agnostic name. Both darwin and linux
can share the same paramters.

source/filesystem_unix_test.go

@@ -0,0 +1,14 @@
+// +build linux,darwin
+package source
+
+//
+// NOTE, any changes here need to be reflected in filesystem_windows_test.go
+//
+var platformBase = "/base/"
+var platformPaths = []TestPath{
+	{"foobar", "foobar", "aaa", "", ""},
+	{"b/1file", "1file", "aaa", "b", "b/"},
+	{"c/d/2file", "2file", "aaa", "d", "c/d/"},
+	{"/base/e/f/3file", "3file", "aaa", "f", "e/f/"},
+	{"section/foo.rss", "foo.rss", "aaa", "section", "section/"},
+}