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Bug #1006634, part 1

Given a string possibly containing characters that are invalid in a
clean url, return a new string, of the allowed length, containing only
valid clean url characters.  If converting utf8 to ascii,
transliterate using the iconv function.

Change-Id: I3dfc505e2be327fb103c4ea59d60082fe3358f0c
Signed-off-by: Richard Mansfield <richard.mansfield@catalyst.net.nz>