rollback the feature of making "ambient upload authority" configurable

rollback the feature of making "ambient upload authority" configurable

This reverses some, but not all, of the changes that were committed in the following set of patches.

rolling back:

Sun Jan 18 09:54:30 MST 2009  toby.murray
  * add 'web.ambient_upload_authority' as a paramater to tahoe.cfg

    M ./src/allmydata/client.py -1 +3
    M ./src/allmydata/test/common.py -7 +9
    A ./src/allmydata/test/test_ambient_upload_authority.py
    M ./src/allmydata/web/root.py +12
    M ./src/allmydata/webish.py -1 +4
Sun Jan 18 09:56:08 MST 2009  zooko@zooko.com
  * trivial: whitespace
  I ran emacs's "M-x whitespace-cleanup" on the files that Toby's recent patch had touched that had trailing whitespace on some lines.

    M ./src/allmydata/test/test_ambient_upload_authority.py -9 +8
    M ./src/allmydata/web/root.py -2 +1
    M ./src/allmydata/webish.py -2 +1
Mon Jan 19 14:16:19 MST 2009  zooko@zooko.com
  * trivial: remove unused import noticed by pyflakes

    M ./src/allmydata/test/test_ambient_upload_authority.py -1
Mon Jan 19 21:38:35 MST 2009  toby.murray
  * doc: describe web.ambient_upload_authority

    M ./docs/configuration.txt +14
    M ./docs/frontends/webapi.txt +11
Mon Jan 19 21:38:57 MST 2009  zooko@zooko.com
  * doc: add Toby Murray to the CREDITS

    M ./CREDITS +4