[libpeas] Fix make clean when $srcdir = $builddir

[Garrett Regier <gregier src gnome org>]

commit d92de7a737d2ec1f3fb971b4affaa10759ad8803
Author: Garrett Regier <garrettregier gmail com>
Date:   Mon Aug 22 11:33:23 2011 -0700

    Fix make clean when $srcdir = $builddir

 tests/Makefile.plugin |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/tests/Makefile.plugin b/tests/Makefile.plugin
index c6c1923..b48d5ef 100644
--- a/tests/Makefile.plugin
+++ b/tests/Makefile.plugin
@@ -14,6 +14,7 @@ all-local:
 
 clean-local:
 	@test -z "$(noinst_PLUGIN)" || \
+	 test $(srcdir) = $(builddir) || \
 	 for plugin in $(noinst_PLUGIN) ; do \
 	   if test -e $(builddir)/$$plugin ; then \
 	     rm -f $(builddir)/$$plugin ; \