mercurial/templates/map-cmdline.compact

mergetool: warn if ui.merge points to nonexistent tool

This adds a warning when ui.merge is configured but points to an
executable that doesn't exist. It gets printed once per fail, but that
seems to be how our other warnings about merge tools are reported.

Differential Revision: https://phab.mercurial-scm.org/D3975

[templates]
ldate = '{label("log.date",
                "{date|isodate}")}'

ldesc = '{label('ui.note log.description',
                      '{desc|strip}')}'
ldescfirst = '{label('ui.note log.description',
                     '{desc|firstline|strip}')}'

changeset = '{lrev}{tags}{bookmarks}{parents}   {lnode}   {ldate}   {luser}\n  {ldescfirst}\n\n'
changeset_quiet = '{lrev}:{lnode}\n'
changeset_verbose = '{lrev}{tags}{parents}   {lnode}   {ldate}   {lauthor}\n  {ldesc}\n\n'
lrev = '{label("log.changeset changeset.{phase}",
              "{rev}")}'
lnode = '{label("log.node",
                "{node|short}")}'
lauthor = '{label("log.user",
                  "{author}")}'
luser = '{label("log.user",
                "{author|user}")}'
start_tags = '['
tag = '{label("log.tag",
              "{tag},")}'
last_tag = '{tag}]'
start_parents = ':'
parent = '{lrev},'
last_parent = '{lrev}'
start_bookmarks = '['
bookmark = '{label("log.bookmark",
                   "{bookmark},")}'
last_bookmark = '{bookmark}]'