find_package: additional test for checking the error message

This patch adds a test which checks the error message, which is
produced in the case that a Config file has set Foo_FOUND to FALSE
by itself.

Alex

Tests/RunCMake/find_package/RunCMakeTest.cmake

@@ -12,3 +12,4 @@ run_cmake(MissingConfigOneName)
 run_cmake(MissingConfigRequired)
 run_cmake(MissingConfigVersion)
 run_cmake(MixedModeOptions)
+run_cmake(SetFoundFALSE)

Tests/RunCMake/find_package/SetFoundFALSE-stderr.txt

@@ -0,0 +1,9 @@
+CMake Warning at SetFoundFALSE.cmake:2 \(find_package\):
+  Found package configuration file:
+
+    .*/Tests/RunCMake/find_package/SetFoundFALSEConfig.cmake
+
+  but it set SetFoundFALSE_FOUND to FALSE so package "SetFoundFALSE" is
+  considered to be NOT FOUND.
+Call Stack \(most recent call first\):
+  CMakeLists.txt:3 \(include\)

Tests/RunCMake/find_package/SetFoundFALSE.cmake

@@ -0,0 +1,2 @@
+set(SetFoundFALSE_DIR "${CMAKE_CURRENT_SOURCE_DIR}")
+find_package(SetFoundFALSE CONFIG)

Tests/RunCMake/find_package/SetFoundFALSEConfig.cmake

@@ -0,0 +1 @@
+set(SetFoundFALSE_FOUND FALSE)