Add SyntaxError test and don't print compilation error to stderr in eval.

mrbgems/mruby-eval/src/eval.c

@@ -112,6 +112,7 @@ create_proc_from_string(mrb_state *mrb, char *s, int len, mrb_value binding, cha
   if (file) {
     mrbc_filename(mrb, cxt, file);
   }
+  cxt->capture_errors = TRUE;
 
   p = mrb_parse_nstring(mrb, s, len, cxt);
 

mrbgems/mruby-eval/test/eval.rb

@@ -44,3 +44,9 @@ assert('rest arguments of eval') do
     Kernel.eval('[\'test\', __FILE__, __LINE__]', nil, 'test.rb', 10)
   end
 end
+
+assert 'eval syntax error' do
+  assert_raise(SyntaxError) do
+    eval 'p "test'
+  end
+end