Log Message:
net/unison: Update to 2.53.1

## Changes in 2.53.1

Released 2023-03-19

  * Repeat mode is more fault tolerant, recovering after temporary
    errors.
  * Preferences "force", "prefer" and related no longer require
    specifying the full root.
  * Improve stopping of update propagation.
  * Enable VT input escape codes in Windows.
  * Respect user-provided CFLAGS, CPPFLAGS, LDFLAGS, LDLIBS.
  * Add build instructions in INSTALL.md (and drop from manual).
  * Add graceful stop in repeat mode - SIGUSR2.
  * Add watch+seconds to 'repeat' preference.