fetch2: unpack revision

Revise the unpack function to have a way to disable the unpack.  This is
based on the work from "Andreas Oberritter <obi@opendreambox.org>", see
http://cgit.openembedded.net/cgit.cgi/openembedded/commit/?id=2bdfe8519eda8067845019a699acdf19a21ba380

In addition, the to_boolean function comes from the work of
"Chris Larson <chris_larson@mentor.com>", see
http://cgit.openembedded.net/cgit.cgi/openembedded/commit/?id=900cc29b603691eb3a077cb660545ead3715ed54

Signed-off-by: Mark Hatle <mark.hatle@windriver.com>

bitbake/lib/bb/utils.py

@@ -831,3 +831,15 @@ def init_logger(logger, verbose, debug, debug_domains):
 
     if debug_domains:
         bb.msg.set_debug_domains(debug_domains)
+
+def to_boolean(string, default=None):
+    if not string:
+        return default
+
+    normalized = string.lower()
+    if normalized in ("y", "yes", "1", "true"):
+        return True
+    elif normalized in ("n", "no", "0", "false"):
+        return False
+    else:
+        raise ValueError("Invalid value for to_boolean: %s" % string)