make failure if Check not installed

[carns]

If you compile libevfibers without first installing the "check" unit testing framework, then the build will fail as shown below. The package is easy to install to resolve the problem, but maybe cmake needs to look for that package up front?

libevfibers/test/init.c:20:19: fatal error: check.h: No such file or directory
 #include <check.h>
                   ^
compilation terminated.
test/CMakeFiles/evfibers_test.dir/build.make:54: recipe for target 'test/CMakeFiles/evfibers_test.dir/init.c.o' failed

[Lupus]

In general agreed. Will dig into this when I have a spare minute.