[grilo-plugins] tests: Add a prototype to avoid a C warning

[Murray Cumming <murrayc src gnome org>]

commit a559ee6e4452607725131d3395aec9e1e70ddb13
Author: Murray Cumming <murrayc murrayc com>
Date:   Tue Dec 4 11:32:05 2012 +0100

    tests: Add a prototype to avoid a C warning

 test/test_tmdb_full_resolution.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/test/test_tmdb_full_resolution.c b/test/test_tmdb_full_resolution.c
index 69f571f..47398b3 100644
--- a/test/test_tmdb_full_resolution.c
+++ b/test/test_tmdb_full_resolution.c
@@ -27,6 +27,8 @@
 
 #define TMDB_PLUGIN_ID "grl-tmdb"
 
+const char *iso_date (const GDateTime *date, char **strbuf);
+
 /** Compare the floats.
  * A simple == will fail on values that are effectively the same,
  * due to rounding issues.