How to transpose a custom slur

[Marten Visser]

Hi all,

When transposing a score, how can I make sure that custom slurs will also 
get transposed? Is there any way to read out how much the notes in the 
score have moved up/down, so that I can use that as a variable in the 
custom slur definition?

Please see the example below how a custom slur becomes ugly when 
transposing from c to e.

Thanks for your time and effort. 
Regards,
Marten

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%{
How to do transposition of custom slur?
%}

\version "2.16.2"

myMusic = {
        \once\override Slur #'control-points = #'((1 . 1.5) (4 . 3.5) (9 . 
3.5) (11 . 1))
        bes8.[( c32 bes] as2.)
}

\score {
        <<
                \new Staff {
                        \key c \minor
                        \new Voice { \transpose c e \relative c'' \myMusic }
                }
        >>
        \layout {}
}