Allow 'a'-lines which don't start with 'a' for backward compatibility.
Allow 'a'-lines which don't start with 'a' for backward compatibility.

The removed bridgedb.Bridges.parseORAddressLine() function was able to take a
networkstatus line which started with 'a' or didn't. It's a mess to change all
the code, so for now just log a warning when we recieve a line in
bridgedb.parse.networkstatus.parseALine() which doesn't start with 'a'.

wfn/bridgedb,mmaker/bridgedb,wfn/bridgedb,mmaker/bridgedb,pagea/bridgedb,pagea/bridgedb