Issue #18: Fixed Delete() function

properties.go

diff --git a/properties.go b/properties.go
index 50209d8..1872abc 100644
--- a/properties.go
+++ b/properties.go
@@ -624,7 +624,7 @@
 	newKeys := []string{}
 	for _, k := range p.k {
 		if k != key {
-			newKeys = append(newKeys, key)
+			newKeys = append(newKeys, k)
 		}
 	}
 	p.k = newKeys

properties_test.go

diff --git a/properties_test.go b/properties_test.go
index 0d61be0..5eb4b45 100644
--- a/properties_test.go
+++ b/properties_test.go
@@ -827,6 +827,8 @@
 	c.Check(len(p.m), Equals, 1)
 	c.Check(len(p.c), Equals, 0)
 	c.Check(len(p.k), Equals, 1)
+	c.Assert(p.k[0], Equals, "second")
+	c.Assert(p.m["second"], Equals, "key")
 }
 
 func (s *TestSuite) TestDeleteUnknownKey(c *C) {