Do not preserve registers by default when exec/eval in a non draft context

Fixes #700

src/commands.cc

@@ -1395,8 +1395,10 @@ void context_wrap(const ParametersParser& parser, Context& context, Func func)
     const bool no_hooks = parser.get_switch("no-hooks") or context.user_hooks_disabled();
     const bool no_keymaps = not parser.get_switch("with-maps");
 
+    const bool save_regs_by_default = (bool)parser.get_switch("draft") or
+                                      (bool)parser.get_switch("buffer");
     Vector<RegisterRestorer> saved_registers;
-    for (auto& r : parser.get_switch("save-regs").value_or("/\"|^@"))
+    for (auto& r : parser.get_switch("save-regs").value_or(save_regs_by_default ? "/\"|^@" : ""))
         saved_registers.emplace_back(r, context);
 
     ClientManager& cm = ClientManager::instance();

test/run

@@ -33,7 +33,7 @@ main() {
         set global autoshowcompl false
         try %{ source rc }
         try %{
-            exec '%s%\(\K[^)]+<ret><c-s>ld<a-t>(hHdi<c-u><esc><c-o>'
+            exec -save-regs '/' '%s%\(\K[^)]+<ret><c-s>ld<a-t>(hHdi<c-u><esc><c-o>'
         } catch %{ exec gg }
         hook global RuntimeError .+ %{
             echo -debug -- error: %val{hook_param}