Bump version to 8.1.0509

- 8.1.0498: /etc/gitconfig not recognized at a gitconfig file. Add
  pattern to filetype detection. (closes #3568)
- 8.1.0499: :2vimgrep causes an ml_get error Pass tomatch pointer
  instead of value. (Yegappan Lakshmanan)
- 8.1.0500: Cleaning up in src/tee may not always work. Use "rm" when
  appropriate. (Michael Soyka, closes #3571)
- 8.1.0501: Cppcheck warns for using array index before bounds check.
  Swap the conditions. (Dominique Pelle)
- 8.1.0502: Internal diff fails when diffing a context diff. (Hirohito
  Higashi) Only use callback calls with one line. (closes #3581)
- 8.1.0503: Missing change to diff test. (Hirohito Higashi) Add the
  missing test function.
- 8.1.0504: When CTRL-C is mapped it triggers InsertLeave. Make CTRL-C
  behave the same way when typed or used in a mapping.
- 8.1.0505: Filter command test may fail if helplang is not set. Set
  'helplang' for the test. (James McCoy, closes #3591)
- 8.1.0506: Modeline test fails when run by root. Set 'modeline' for the
  test. (James McCoy, closes #3592)
- 8.1.0507: .raml files not properly detected. Recognize .raml as raml
  instead of yaml. (closes #3594)
- 8.1.0508: Suspend test fails when run by root. Accept both '$' and '#'
  for the prompt. (James McCoy, closes #3590)
- 8.1.0509: Checking cwd not accessible fails for root. (James McCoy)
  Skip this part of the test for root. (closes #3595)