FFe: multiarch support of qt4-x11 dependencies (libmng, lcms)

Two dependency library packages need to be converted for multiarch in order for libqtgui4 to be multiarch co-installable: libmng, and lcms.

Risk: both of these are very simple libraries with no plugins, so the risk of runtime regression is small. (Only from something trying to dlopen() a path it shouldn't.) lcms has a .la file with one reference in the archive, in the 'libdevil-dev' package; a no-change rebuild of this package is trivial to do to fix this. Otherwise, the only risks are from reverse-build-dependencies of the libraries having build systems that make wrong assumptions about how to find the libraries. lcms has a number of reverse-build-dependenices, but the vast majority of these have traditional build systems that are multiarch-proofed so the risk is low. The highest risk may be from openjdk-6, but openjdk-6 has also built successfully without incident after multiarch conversion of a number of its other build dependencies so the risk here should also be low - and manageable in the unlikely case of any breakage. If necessary, I can do test rebuilds here of all the reverse-dependencies before uploading, although the risk is low enough and we're soon enough after feature freeze that I believe it would be better to upload first and identify any regressions in parallel.

Benefit: together with a fix for bug #825689, this is sufficient to allow all the qt dependencies of skype to be installed in multiarch configuration, eliminating a major reason for users to install ia32-libs on their systems.