A little violations of DRY

[Dmitry]

invalid_name_error variable never used:

channels/channels/layers.py

Lines 142 to 145 in 6af1bc3

 invalid_name_error = ( 
     "{} name must be a valid unicode string containing only ASCII " 
     + "alphanumerics, hyphens, underscores, or periods." 
 ) 

But it supposed to be used here?

channels/channels/layers.py

Lines 156 to 159 in 6af1bc3

 raise TypeError( 
     "Channel name must be a valid unicode string containing only ASCII " 
     + "alphanumerics, hyphens, or periods, not '{}'.".format(name) 
 ) 

So that TypeError shows that we can't use underscores, but we actually can (according regexps above).
Actually we can reuse that variable here (since both regexps almost identical) just using different prefixes in error message ("Channel" and "Group")

channels/channels/layers.py

Lines 165 to 168 in 6af1bc3

 raise TypeError( 
     "Group name must be a valid unicode string containing only ASCII " 
     + "alphanumerics, hyphens, or periods." 
 )