tests: demonstrate that no requested merge tool is ignored if missing
If you explicitly configure a merge tool, it seems wrong that we don't
even warn if we can't find it. This patch adds a test case that
demonstrates that.
Differential Revision: https://phab.mercurial-scm.org/D3974
# See http://EditorConfig.org for the specification
root = true
[*.py]
indent_size = 4
indent_style = space
trim_trailing_whitespace = true
[*.{c,h}]
indent_size = 8
indent_style = tab
trim_trailing_whitespace = true
[*.t]
indent_size = 2
indent_style = space
trim_trailing_whitespace = false