Include test for relative URL.

src/zc/buildout/extends-cache.txt

@@ -457,12 +457,18 @@ used:
 ... extends = %sbase.cfg
 ... bar = foo
 ... """ % server_url)
+>>> write(server_data, 'baseC.cfg', """\
+... [buildout]
+... extends-cache = cache
+... extends = baseB.cfg
+... bar = foo
+... """)
 >>> write('buildout.cfg', """\
 ... [buildout]
 ... extends-cache = cache
 ... newest = true
-... extends = %sbaseA.cfg %sbaseB.cfg
-... """ % (server_url, server_url))
+... extends = %sbaseA.cfg %sbaseB.cfg %sbaseC.cfg
+... """ % (server_url, server_url, server_url))
 >>> print system(buildout + " -n")
 Unused options for buildout: 'bar' 'foo'.
 
@@ -480,6 +486,7 @@ a better solution would utilise the logging already done by the utility.)
 The URL http://localhost/baseA.cfg was downloaded.
 The URL http://localhost/base.cfg was downloaded.
 The URL http://localhost/baseB.cfg was downloaded.
+The URL http://localhost/baseC.cfg was downloaded.
 Unused options for buildout: 'bar' 'foo'.
 
 >>> zc.buildout.download.Download.download = old_download