kernel: Skip sendfile tests that force async threads

The tests have to be skipped when the emulator running the tests does
not have any async threads.
Add hyperlinks to modules in reference manual for kernel application

This makes the pointers to other reference manuals consistent
throughout this page.
Store expanded config in application_controller:change_application_data

If the Config given to application_controller:change_application_data
included other config files, it was only expanded for already existing
(loaded) applications. If an upgrade added a new application which had
config data in an included config file, the new application did not
get correct config data.

This is now changed so config data will be expanded for all
applications.
Merge branch 'siri/ac-change_app_data/OTP-11864' into maint

* siri/ac-change_app_data/OTP-11864:
  Store expanded config in application_controller:change_application_data
Update kernel, stdlib and sasl appup tests

Add test of update instructions from current major to current
minor. Earlier only previous major to current was tested.
kernel: Fix erts_debug:size/1 to handle Map sizes
Merge branch 'lukas/kernel/fix_sendfile_no_async_tests/OTP-11903' into maint

* lukas/kernel/fix_sendfile_no_async_tests/OTP-11903:
  kernel: Skip sendfile tests that force async threads
Merge branch 'siri/cuddle-with-tests' into maint

* siri/cuddle-with-tests:
  Fix regexp in release_handler test so versions are correctly replaced
  Update kernel, stdlib and sasl appup tests
  Minor update to test_server for finding old releases
inet: fix typo in inet:getstat/2 doc

The word 'received' in 'send_dvi' option description seems to be
copy-pasted and not removed
Merge branch 'egil/fix-erts_debug-size/OTP-11923' into maint

* egil/fix-erts_debug-size/OTP-11923:
  erts: Update preloaded erts_internal.beam
  erts: Add spec for erts_internal:map_to_tuple_keys/1
  erts: Add testcase for erts_debug:size/1 Map terms
  kernel: Fix erts_debug:size/1 to handle Map sizes
  erts: Add erts_internal:map_to_tuple_keys/1
Merge branch 'dz/inet_getstat_doc_typo_fix' into maint

* dz/inet_getstat_doc_typo_fix:
  inet: fix typo in inet:getstat/2 doc
Teach code:del_path/1 to ignore superfluous slashes

The following sequence will NOT leave the code path unchanged:

  code:add_path("/some/app/"),
  .
  .
  .
  code:del_path("/some/app/")

The reason is that code:add_path/1 will normalize the path name
(removing the trailing slash), while code:del_path/1 does not
normalize the path before searching for it in the code path.
application_SUITE: Clean up the code after the test is done
Make pre-loaded modules permanently sticky

Modules in the kernel, stdlib, and compiler applications are by
default "sticky", meaning that the code server will refuse to
re-load them.

The pre-loaded modules (those that are part of the run-time system
itself, such as 'erlang') are, however, not sticky. They used to be
sticky a long time ago when the pre-loaded modules were part of
the kernel application. Now they are part of the erts application.

Since re-loading a pre-loaded module can be catastrophic (especially
re-loading the 'erlang' module), the pre-loaded modules must be
sticky. Furthermore, it should not be allowed to unstick them.

The sticky_dir/1 test case in code_SUITE is never actually run and
is broken. Rewrite it.
Allow unsticking pre-loaded modules

Commit ed06dd12ea74018b902a2c4c7924313d23cedb75 made pre-loaded
modules (such as erlang) sticky, and also made it impossible to
unstick them to prevent them from ever be reloaded.

It turns out that there are tools that may want to instrument
the erlang module (such as concuerror), so making it
impossible to unstick modules is harsh. Therefore, revert the
part of the commit that prevented unsticking the pre-loaded
modules.
Remove documentation and stub for non-exist file:file_info/1

file:file_info/1 was removed a long time ago, but its
documentation was not removed.
Merge branch 'bjorn/kernel/remove-file_info-vestiges/OTP-11982' into maint

* bjorn/kernel/remove-file_info-vestiges/OTP-11982:
  Remove documentation and stub for non-exist file:file_info/1
Prepare release