[petsc-users] configure: Include urlopen exception string in download failure message

[Aagaard, Brad T via petsc-users]

The current implementation of Retrival.tarballRetrieve() does not capture the 
error string from an exception raised in a call to urlopen(). This makes it 
difficult to diagnose download failures. Can you add the error string from the 
exception to the download failure message (maybe as an optional argument to 
getDownloadFailureMessage())? This is at lines 205-208 of 
config/BuildSystem/retrieval.py.

Thanks,
Brad