Log Message:
net/unison: Update to 2.51.3

Upstream NEWS content

## 2.51.3
  * ocaml support is now from 4.05 to 4.11
  * reduction of stack usage by proper tail recursion
  * MS Windows build improvements
  * Some nontrivial changes to profile parsing (G.raud Meyer)
    ’=’ has been considered whitespace until now: several
    following chars are considered as only one; trailing chars are
    discarded; any non emty sequence of char is splitting. This is
    non standard and leads to confusion, for example -ignore==
    ’Name .*=*’ is valid when -ignore=’Name .*=*’ is not, and
    worse -ignore=’Name *=’ is the same as -ignore=’Name *’. The
    parser now takes just a single ’=’ as delimiter after the
    option name. Other = characters are considered as part of the
    value being assigned to the option.
  * Numerous improvements to the text user-interface (G.raud Meyer)
    New key-commands that restrict the display to a set of
    "matching" items: ones that are offering to propagate changes
    in a particular direction, conflicts, files to be merged,
    etc., plus several more useful key-commands. Type "?" to
    Unison to see all available commands.