Bug#900819: gimp: Dependency on liblcms2-2 needs tightening

[Jeremy Bicha]

Control: reopen -1
Control: forcemerge -1 906731

Well a simple rebuild didn't work. I'm not sure what more we should be
doing here. It feels clumsy if we need to bump the version of
liblcms2-dev that gimp Build-Depends on every time there we do a gimp
upload after a new lcms2 version in Debian.

Thanks,
Jeremy Bicha