MDEV-6657: Poor plan choice for ORDER BY key DESC optimization...

The problem was caused by the following scenario:
- range optimizer picks an index IDX1 which doesn't match the ORDER BY ...
  LIMIT clause.
- test_if_skip_sort_order() decides to switch to index IDX2 which matches
  the ORDER BY ... LIMIT.
- it runs SQL_SELECT::test_quick_select() for the second time to produce
  an quick select for IDX2.
- However, test_quick_select() would figure that full index scan on IDX1
  is still cheaper (its calculations ignore the LIMIT n).

Fixed this by
- passing force_quick_range=true to test_quick_select()
- in test_quick_select, don't consider full index scans if the mentioned
  parameter is true.

Numerous changes in .result files are caused by test_quick_select() being
run after "early/late NULLs filtering" feature has injected NOT NULL
condition.
Merge 10.1 into bb-10.1-mdev6657
MDEV-6402: Optimizer doesn't choose best execution plan when composite...

Fix test_if_skip_sort_order() logic:
WHEN
we use index X, which doesn't produce needed ordering, but there is
an index Y which does and has the same prefix as used prefix of X
THEN
don't just switch to using ref access on Y. If range(Y) would use more
key parts, use range(Y).
Better comments
Merge ../10.1-mdev6402 into bb-10.1-orderby-fixes
Merge ../10.1-mdev6657 into bb-10.1-orderby-fixes
Cmake Problem fix
gitignore
fixed unit tests
Fixed failing test temp_table_frm

The problem was that the internal temporary table created
for information_schema overflow to MyISAM because it has
a row width of > 3000 characters, which filled the in memory
temporary tables.
Fix was to increase size for the heap table.
Better comments
Merge branch '10.1' of github.com:MariaDB/server into 10.1
MDEV-6788: The variable 'role' is being used without being initialized at sql_acl.cc:8840

[Re-commit in git]
Don't check the value of 'role' variable in the cases where we don't need
it. (it may be marked as uninitialized and we get a runtime error).
MDEV-6788: The variable 'role' is being used without being initialized at sql_acl.cc:8840

[re-commit in git]
Second variant of the fix: reduce the scope of 'role' variable
MDEV-6790: 10.1: debian build failure
Updated 33_scripts__mysql_create_system_tables__no_test.dpatch
to reflect user.default_role.
Fix for syntax error in debian control file.
Better comments about KEY::ext_key_part_map
Merge branch '10.1' of github.com:MariaDB/server into 10.1
wsrep-related changes: removed some unnecessary files & minor modifications.
Fix test failures seen on
-- innodb-wl5522-debug-zip (path differences win/unix)
-- innodb_defragment_fill_factor (stabilise)
-- innodb_force_pk (case difference win/unix)