Typo correction for d-i i18n and l10n Guide

[Tapio Lehtonen <tale@iki.fi>]

345c345
< present. This explains why this script must always been monitored even
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> present. This explains why this script must always be monitored even
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< First of all, before doing any work, the script open a special file
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> First of all, before doing any work, the script opens a special file
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< This mechanims gives all &d-i; developers with commit access to the
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> This mechanism gives all &d-i; developers with commit access to the