[BUG?] libxrender-dev checking is missing

[Miguel Ojeda]

Hi KDE-devs!

For kdelibs-4.2.0/kfile/kfilepreviewgenerator.cpp, libxrender-dev is needed;
however, the configure script does not seem to warn about that it is missing.

Moreover, at lines 724~726, XRender*() calls are undefined while linking,
so I assume that the library is not being properly linked as the configure
script does not seem to care about it.

Please review this issue if it is not my fault. Thank you for KDE 4.2! :)

PS: Please CC me, I'm not subscribed.

Miguel Ojeda