Problem:    The code style has to be checked manually.
Solution:   Add basic code style checks in a test.  Fix or avoid uncovered
            problems.

Problem:    Code is indented more than necessary.
Solution:   Use an early return where it makes sense. (Yegappan Lakshmanan,
            closes #11792)

Problem:    Code uses too much indent.
Solution:   Use an early return. (Yegappan Lakshmanan, closes #11747)

Problem:    Using one window for executing autocommands is insufficient.
Solution:   Use up to five windows for executing autocommands.

Problem:    Redraw flags are not named specifically.
Solution:   Prefix "UPD_" to the flags, for UPDate_screen().

Problem:    Code has more indent than needed.
Solution:   Use continue and return statements. (closes #10824)

Problem:    Invalid memory access in diff mode with "dp" and undo.
Solution:   Make sure the line number does not go below one.

Problem:    Accessing freed memory with diff put.
Solution:   Bail out when diff pointer is no longer valid.

Problem:    Invalid memory access after diff buffer manipulations.
Solution:   Use zero offset when change removes all lines in a diff block.

Problem:    Crash when deleting buffers in diff mode.
Solution:   Recompute diffs later.  Skip window without a valid buffer.