Bug#482268: kate: kwrite freezes on certain replacement

[Steve Cotton <steve@s.cotton.clara.co.uk>]

I'm still investigating, but have some results and a
simplification of the test case:

>   Text to find: '[ab]'
>           as a regexp

"As a regexp" is needed, but the text to find can be simply 'a'.

>   Replace with: '\\0'
>	   with backreferences allowed

Kate's dialog calls backrefs "placeholders".

Following these instructions, you must also click "continue from
beginning" when prompted.


Behaviour with various replacement strings:
    \1\1  (with text to find '([ab])'
        Works correctly (result is 'aabbc')

    \1\1  (with text to find '[ab]'
        Correct error message that the pattern lacks a capture.

    \\z
        '\\z' appears in the text - the escape sequence isn't
        converted to single backslash.

    \\0
    \\1
    \\9
        All of these result in a freeze.