fix conflict with stdin symbol in headers

Index: test/engine/imap-db/imap-db-database-test.vala
--- test/engine/imap-db/imap-db-database-test.vala.orig
+++ test/engine/imap-db/imap-db-database-test.vala
@@ -179,16 +179,16 @@ class Geary.ImapDB.DatabaseTest : TestCase {
             GLib.SubprocessFlags.STDIN_PIPE,
             "tar", "-xJf", "-", "-C", dest.get_path()
         );
-        GLib.OutputStream stdin = untar.get_stdin_pipe();
+        GLib.OutputStream stdinx = untar.get_stdin_pipe();
 
         uint8[] buf = new uint8[4096];
         ssize_t len = 0;
         do {
             len = bytes.read(buf);
-            stdin.write(buf[0:len]);
+            stdinx.write(buf[0:len]);
         } while (len > 0);
 
-        stdin.close();
+        stdinx.close();
 
         untar.wait();
     }