win32: improve the performance of win32.unlink() over CIFS Emulating POSIX unlink() behavior with os.rename() and os.unlink() is often slow especially over CIFS from Windows clients due to its protocol overhead. This patch changes win32.unlink() to try first an exclusive open with the Win32 delete-on-close flag, and if a sharing violation is detected, to fall back to the original emulation. This patch also removes a test with os.path.isdir() since we expect opening a directory shall fail as os.unlink() would. Example measurements (repeated 3-times after 1-time calibration): (Without this patch: hg update from null to default) 127 files updated, 0 files merged, 0 files removed, 0 files unresolved time: real 19.871 secs (user 0.328+0.000 sys 1.794+0.000) time: real 19.622 secs (user 0.312+0.000 sys 2.044+0.000) time: real 19.138 secs (user 0.250+0.000 sys 1.872+0.000) (Without this patch: hg update from default to null) 0 files updated, 0 files merged, 127 files removed, 0 files unresolved time: real 35.158 secs (user 0.156+0.000 sys 2.512+0.000) time: real 35.272 secs (user 0.250+0.000 sys 2.512+0.000) time: real 36.569 secs (user 0.203+0.000 sys 2.387+0.000) (With this patch: hg update from null to default) 127 files updated, 0 files merged, 0 files removed, 0 files unresolved time: real 17.893 secs (user 0.328+0.000 sys 1.700+0.000) time: real 18.512 secs (user 0.265+0.000 sys 1.529+0.000) time: real 20.238 secs (user 0.312+0.000 sys 1.685+0.000) (With this patch: hg update from default to null) 0 files updated, 0 files merged, 127 files removed, 0 files unresolved time: real 12.312 secs (user 0.250+0.000 sys 0.811+0.000) time: real 12.471 secs (user 0.156+0.000 sys 0.889+0.000) time: real 9.727 secs (user 0.125+0.000 sys 0.858+0.000)