patch 8.0.0563: crash when getting the window position in tmux

Problem:    Crash when getting the window position in tmux. (Marvin Schmidt)
Solution:   Add t_GP to the list of terminal options. (closes vim#1627)

patch 8.0.0562: not enough test coverage for syntax commands

Problem:    Not enough test coverage for syntax commands.
Solution:   Add a few more tests. (Dominique Pelle, closes vim#1624)

patch 8.0.0561: undefined behavior when using backslash after empty line

Problem:    Undefined behavior when using backslash after empty line.
Solution:   Check for an empty line. (Dominique Pelle, closes vim#1631)

patch 8.0.0560: :windo allows for ! but it's not supported

Problem:    :windo allows for ! but it's not supported.
Solution:   Disallow passing !. (Hirohito Higashi)

patch 8.0.0559: setting ttytype to xxx does not always fail

Problem:    Setting ttytype to xxx does not always fail as expected. (Marvin
            Schmidt)
Solution:   Catch both possible errors. (closes vim#1601)

patch 8.0.0558: :ownsyntax is not tested

Problem:    The :ownsyntax command is not tested.
Solution:   Add a test. (Dominique Pelle, closes vim#1622)

patch 8.0.0557: GTK: using static gravities is not useful

Problem:    GTK: using static gravities is not useful.
Solution:   Remove setting static gravities. (Kazunobu Kuriyama)

patch 8.0.0556: getting window position fails if GUI and term possible

Problem:    Getting the window position fails if both the GUI and term
            code is built in.
Solution:   Return after getting the GUI window position. (Kazunobu Kuriyama)

patch 8.0.0555: toupper/tolower test fails on OSX without Darwin

Problem:    Toupper/tolower test fails on OSX without Darwin.
Solution:   Skip that part of the test also for OSX. (Kazunobu Kuriyama)

patch 8.0.0554: toupper and tolower don't work properly for Turkish

Problem:    Toupper and tolower don't work properly for Turkish when 'casemap'
            contains "keepascii". (Bjorn Linse)
Solution:   When 'casemap' contains "keepascii" use ASCII toupper/tolower.