Fix issue #24: update PWL more compatibly
Fix issue #24: update PWL more compatibly

Add a newline before the new word only if there isn’t one there already,
then add a newline after. This is compatible with more update strategies,
e.g. hunspell always adds the new word and then a newline.

This enables users to share dictionaries between different spell-checkers
with symlinks.

This is also compatible with enchant <= 1.6.0, in which case (harmless)
empty lines may be added to the PWL (e.g. if enchant 1.6.1 adds a word, then
enchant 1.6.0).

albbas/enchant,rrthomas/enchant,AbiWord/enchant,rrthomas/enchant,albbas/enchant,rrthomas/enchant,albbas/enchant,AbiWord/enchant,rrthomas/enchant,albbas/enchant,AbiWord/enchant,AbiWord/enchant