fix parsing Makefile dependencies when they spanned multiple lines

spec/rscons/environment_spec.rb

@@ -0,0 +1,24 @@
+module Rscons
+  describe Environment do
+    describe '.parse_makefile_deps' do
+      it 'handles dependencies on one line' do
+        File.should_receive(:read).with('makefile').and_return(<<EOS)
+module.o: source.cc
+EOS
+        env = Environment.new
+        env.parse_makefile_deps('makefile', 'module.o').should == ['source.cc']
+      end
+
+      it 'handles dependencies split across many lines' do
+        File.should_receive(:read).with('makefile').and_return(<<EOS)
+module.o: module.c \\
+  module.h \\
+  other.h
+EOS
+        env = Environment.new
+        env.parse_makefile_deps('makefile', 'module.o').should == [
+          'module.c', 'module.h', 'other.h']
+      end
+    end
+  end
+end