Re: enable icu support by default in libxml2

[nia <nia%NetBSD.org@localhost>]

my problem with icu is not necessarily from a size standpoint but a
stability standpoint. icu is like boost, etc. not-infrequent API/ABI
breaks, and a shlib bump on every update so everything needs to be
rebuilt.

this is not really helpful for security updates (since if upstream
publishes a new release with critical fixes every dependent package
needs to be rebuilt and tested to make sure it does actually still
build, backports are harder, etc), and also makes developing
pkgsrc-current on a smaller machine harder. 

in harfbuzz i have split off the icu-depedent part of it into a
separate package.

i saw from a quick scan of its headers that libxml2 exposes
icu-dependent parts as part of its public API, but if no separation
at all is possible then that's quite a shame. i always prefer
separate packages to PKG_OPTIONS, especially since revbump 
doesn't handle PKG_OPTIONS.

cheers,
nia