use internal merge tool when specified for a merge-pattern in hgrc
It is possible to specify in the hgrc file that one of the internal merge
tools (internal:fail, internal:local or internal:other) be used for
performing merges on files matching a given pattern. However, this setting
is not being acted upon (the merge tool is not found). This patch fixes that.
abort: Failed to parse .../t/.hg/hgrc
File contains no section headers.
file: .../t/.hg/hgrc, line: 1
'invalid\n'