Pager should allow changing the "number of items per page" (and allow "show all")

Problem/Motivation

There is no way for a site to set how many items can be displayed using pager. Currently the default is 10 items.

Proposed resolution

It would be nice to allow the site admin or end user to set how many items they want to display per page using pager.

Remaining tasks

Decide on the proper implementation.
Four methods have been proposed.

1. Allow the site admin to set the number a items to view per page using pager. Also increase the default to 50.
   
2. Allow the end user to set the number of items per page when using pager.
   
3. Abandon the pager concept wholesale and aim for infinite scroll: #1488866: Redesign pagers for administrative lists. →
4. Go from a number based pager to alphabetical based.
   

User interface changes

Admins or users will be able to set a number of items to display per page using pager, and alphabetical list, or an infinite scroll approach.

Questions:

1. Which of these methods, or some combination of them, is preferred?
2. What numbers should be used for min/max values, if any?
3. Where do we want the validation performed?

Original description

It will be nicer to have an option that users can select by themselves how many records can be displayed on a page, such as 5, 15, 50, or all records. This feature is actually very common.

The best place I have thought is to add the feature to the pager.

I have implemented this feature on my site one year ago when I was new to Drupal. As it requires many changes not only in pager.inc but also somewhere else, I expect that Drupal developers can do a better job than me.

I look forward to see this common feature in Drupal 4.7.