Replaced usage of urlopen.read(), which isn't guaranteed to return all of the downloaded bytes, with urlopen.readlines(), which (I believe) does have that guarantee.  This should fix the rash of mysteriously-failing prebuilds.  In the process, added some better error messaging about whether the local template has the parse error, or the master on the network.  Also some reorganization.  Reviewed by Tess and Leyla.