* john/erts/lists_subtract_fixes/OTP-15938/OTP-15939:
  erts: Fix integer overflow in loader
  erts: Fix integer overflow in list subtraction

CMP_TERM returned an `Sint`, which overflowed the `int` used in
erl_rbtree for storing the comparison, causing list subtraction to
behave strangely.

* hasse/stdlib/chars_limit_bug/OTP-15875/ERL-967:
  stdlib: Fix a bug concerning io_lib option 'chars_limit'

# Conflicts:
#	lib/stdlib/test/io_SUITE.erl

See also https://bugs.erlang.org/browse/ERL-967.

See also https://bugs.erlang.org/browse/ERL-957.

into sverker/maint/ets-no-mbuf-trapping/OTP-15660

Many heap fragments do no longer make the GC slow.

Even worse, we are not guaranteed that a yield will provoke a GC
removing the fragments, which might lead to a one-yield-per-bucket
scenario if the heap fragment(s) still remains after each yield.

Avoid traversing all of the list/string when only part of it will be
used. An explicit check that the list is flat is needed since
string:slice() accepts deep lists and more.

* hasse/stdlib/optimize_calendar_rfc3339/OTP-15630:
  stdlib: Optimize calendar:system_time_to_rfc3339()

Not using io_lib for formatting makes the conversion several times
faster.