patch 8.0.0206: test coverage for :retab insufficient

Problem:    Test coverage for :retab insufficient.
Solution:   Add test for :retab. (Dominique Pelle, closes vim#1391)

patch 8.0.0205: wrong behavior after :undojoin

Problem:    After :undojoin some commands don't work properly, such as :redo.
            (Matthew Malcomson)
Solution:   Don't set curbuf->b_u_curhead. (closes vim#1390)

patch 8.0.0204: compiler warns for uninitialized variable

Problem:    Compiler warns for uninitialized variable. (Tony Mechelynck)
Solution:   When skipping set "id" to -1.

patch 8.0.0203: order of complication flags is sometimes wrong

Problem:    Order of complication flags is sometimes wrong.
Solution:   Put interface-specific flags before ALL_CFLAGS. (idea by Yousong
            Zhou, closes vim#1100)

patch 8.0.0202: no test for invalid syntax group name

Problem:    No test for invalid syntax group name.
Solution:   Add a test for group name error and warning.

patch 8.0.0201: completion of highlight groups includes cleared names

Problem:    When completing a group name for a highlight or syntax command
            cleared groups are included.
Solution:   Skip groups that have been cleared.

patch 8.0.0200: some syntax arguments are not tested

Problem:    Some syntax arguments are not tested.
Solution:   Add more syntax command tests.

patch 8.0.0199: compiler warnings for libcall

Problem:    Warning for an unused parameter when the libcall feature is
            disabled.  Warning for a function type cast when compiling with
            -pedantic.
Solution:   Add UNUSED.  Use a different type cast. (Damien Molinier)

patch 8.0.0198: some syntax arguments take effect even after "if 0"

Problem:    Some syntax arguments take effect even after "if 0". (Taylor
            Venable)
Solution:   Properly skip the syntax statements.  Make "syn case" and "syn
            conceal" report the current state.  Fix that "syn clear" didn't
            reset the conceal flag.  Add tests for :syntax skipping properly.

patch 8.0.0197: system() test skips some parts for MS-Windows

Problem:    On MS-Windows the system() test skips a few parts.
Solution:   Swap single and double quotes for the command.