lh_chroot_localization: icedove-locale-* breaks Squeeze build

[intrigeri <intrigeri@boum.org>]

Hi,

the icedove-locale-* transitional packages have been removed from
Squeeze, so lh_chroot_localization should install the icedove-l10n-*
packages on >=squeeze instead. LH_DISTRIBUTION must probably be tested
in case --distribution etch must still be supported, as these new
packages names were not in etch.

bye,
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