bitbake fetch/git.py: Don't use master as a tag

git-svn-id: https://svn.o-hand.com/repos/poky/trunk@2501 311d38ba-8fff-0310-9ca6-ca027cbcb966

bitbake/lib/bb/fetch/git.py

@@ -51,7 +51,7 @@ class Git(Fetch):
             ud.proto = ud.parm['protocol']
 
         tag = data.getVar("SRCREV", d, 0)
-        if 'tag' in ud.parm:
+        if 'tag' in ud.parm and len(tag) == 40:
             ud.tag = ud.parm['tag']
         elif tag and "get_srcrev" not in tag and len(tag) == 40:
             ud.tag = tag