add :check_cpppath option to check_c_header and check_cxx_header

configuration methods
add :check_d_import_path option to check_d_import configuration method - #107

build_tests/configure/check_c_header_cpppath.rb

@@ -0,0 +1,10 @@
+configure do
+  check_c_header "string.h", check_cpppath: ["./usr1"]
+  check_c_header "frobulous.h", check_cpppath: ["./usr2"]
+end
+
+build do
+  Environment.new do |env|
+    env.Object("test.o", "test.c")
+  end
+end

build_tests/configure/check_cxx_header_cpppath.rb

@@ -0,0 +1,10 @@
+configure do
+  check_cxx_header "string.h", check_cpppath: ["./usr1"]
+  check_cxx_header "frobulous.h", check_cpppath: ["./usr2"]
+end
+
+build do
+  Environment.new do |env|
+    env.Object("test.o", "test.cc")
+  end
+end

build_tests/configure/check_d_import_d_import_path.rb

@@ -0,0 +1,10 @@
+configure do
+  check_d_import "std.stdio", check_d_import_path: ["./usr1"]
+  check_d_import "frobulous", check_d_import_path: ["./usr2"]
+end
+
+build do
+  Environment.new do |env|
+    env.Object("test.o", "test.d")
+  end
+end