.editorconfig

filemerge: make capability check for internal tools ignore merge-tools section

This is follow up of 4d7b11877dd0.

Before this patch, capability check of internal merge tools falls back
to _toolbool(), which examines configurations in "merge-tools" section.

But "hg help config" explicitly says that "merge-tools" section
configures external merge tools.

Therefore, this patch makes capability check for internal tools in
hascapability() always ignore configurations in merge-tools section.

In this patch, command line configurations below are added at tests in
tests/test-merge-tools.t, in order to confirm that explicit
configuration is intentionally ignored at tool selection.

  --config merge-tools.:INTERNAL_TOOL.CAPABILITY=true

# 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