JIRA: https://jira.spring.io/browse/INT-4005
* The `<int:queue>` lets declare the `capacity` attribute together
with either `message-store` or `ref` attributes, which it is not
correct
* The `<int:queue>` lets declare the `capacity` attribute together
with either `message-store` or `ref` attributes, which it is not
correct
* The `priority-queue` lets declare the `capacity` attribute
together with the `message-store` attribute, which it is not
correct
* Reference documentation fixed for `channel.adoc` and `jdbc.adoc`,
doing mention about these restrictions
* Minor changes about conventions and formats applied.
Code polishing
8cfb7414ad