KeyCancellation grobs should ignore cue clefs like KeySignature grobs do

KeyCancellation grobs should ignore cue clefs like KeySignature grobs do

For

{
  \key f \major R1 \cueClef bass \key g \major R1 \cueClefUnset
  R1 \cueClef alto \key bes \major R1
}

the cancellation signs for the key changes were erroneously placed in
reference to the current cue clef rather than the main clef while the
key signature itself was properly unimpressed.

[lemzwerg, 2014-05-03 13:58:10]

LGTM.