manpage: fix reference to a defunct option

The change was made with faad40aad92d51290ef2fc4d94277eca89863873.
TOOLS/vf_dlopen/ildetect.sh: remove duplicated assigment
common: fix \x-style escaping

This was rejecting correct escapes and accepting incorrect ones.
player: quote %-starting strings

Leading percent sign is a quote indicator so it needs to be quoted
itself.
DOCS/client_api_examples: qtexample: embedding works on Cocoa
DOCS/client_api_examples: qtexample: set a magic Qt flag

Otherwise, other magic Qt stuff can be magically broken.

(No, I don't know the real reasons for this.)