Make the seek and colorkey examples depend on gtk+-x11 as they use

Original commit message from CVS:
* configure.ac:
* tests/examples/seek/Makefile.am:
* tests/icles/Makefile.am:
Make the seek and colorkey examples depend on gtk+-x11 as they use
GDK_WINDOW_XID.
Fixes the build with gtk+-quartz.
4 files changed