base85: proxy through util module
I'm going to replace hgimporter with a simpler import function, so we can
access to pure/cext modules by name:
# util.py
base85 = policy.importmod('base85') # select pure.base85 or cext.base85
# cffi/base85.py
from ..pure.base85 import * # may re-export pure.base85 functions
This means we'll have to use policy.importmod() function in place of the
standard import statement, but we wouldn't want to write it every place where
C extension modules are used. So this patch makes util host base85 functions.
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