warn about %xx in filenames being misinterpreted

[julian.reschke@…]

Add a warning that certain UAs misinterpret %xx escapes in filenames.

(Unfortunately there's no workaround as those UAs do not accept RFC5987 encoding either)

[julian.reschke@…]

It occurred to me that putting an escape char inside the %xx sequence might disable percent-unescaping. See test case at

​http://greenbytes.de/tech/tc2231/#attwithfnrawpctencaq

Unfortunately, this breaks in all UAs that do not handle escape characters in quoted strings properly (that is, all but Konq and Opera).

[julian.reschke@…]

From [1041]:

point out impl problems wrt to unescaping (not handling backslash in quoted string, misinterpreting %xx) (see #245)

[mnot@…]

Closed in last call process.