Support changing buffer when an edition is in progress

src/context.cc

@@ -170,8 +170,14 @@ void Context::forget_jumps_to_buffer(Buffer& buffer)
 
 void Context::change_buffer(Buffer& buffer)
 {
+    if (&buffer == &this->buffer())
+        return;
+
     if (m_edition_level > 0)
-        throw runtime_error("the current buffer is still being edited");
+    {
+       this->buffer().commit_undo_group();
+       m_edition_level = 0;
+    }
     m_window.reset();
     if (has_client())
         client().change_buffer(buffer);

src/context.hh

@@ -113,15 +113,21 @@ private:
 struct ScopedEdition
 {
     ScopedEdition(Context& context)
-        : m_context(context)
+        : m_context(context), m_buffer(&context.buffer())
     { m_context.begin_edition(); }
 
     ~ScopedEdition()
-    { m_context.end_edition(); }
+    {
+        // If buffer changed, the edition count
+        // was reset.
+        if (m_buffer == &m_context.buffer())
+            m_context.end_edition();
+    }
 
     Context& context() const { return m_context; }
 private:
     Context& m_context;
+    safe_ptr<Buffer> m_buffer;
 };
 
 }