missing check library causes make to fail

[fmhess]

The configure script only generates a warning if the "check" library is not found, saying unit tests will not run. However, a missing check library causes "make" to fail:

$ make
CC test/test_util.o
In file included from ../test/test_util.c:1:0:
../test/test_util.h:7:19: fatal error: check.h: No such file or directory
compilation terminated.
make[1]: *** [test/test_util.o] Error 1
make: *** [all] Error 2

[nickg]

Should be fixed now