filemerge: make warning message more i18n friendly Before this patch, " specified for " part of warning messages (e.g. "couldn't find merge tool TOOL specified for PAT") isn't translatable.

filemerge: show warning about choice of :prompt only at an actual fallback Before this patch, internal merge tool :prompt shows "no tool found to merge FILE" line, even if :prompt is explicitly specified as a tool to be used. This patch shows warning message about choice of :prompt only at an actual fallback, in which case any tool is rejected by capability for binary or symlink. It is for backward compatibility to omit warning message in "changedelete" case.

treemanifest: allow manifestrevlog to take an explicit treemanifest arg Previously we relied on the opener options to tell the revlog to be a tree manifest. This makes it complicated for extensions to create treemanifests and normal manifests at the same time. Let's add a construtor argument to create a treemanifest revlog as well. I considered removing the options['treemanifest'] logic from manifestrevlog entirely, but doing so shifts the responsibility to the caller which ends up requiring changes in localrepo, bundlerepo, and unionrepo. I figured having the dual mechanism was better than polluting other parts of the code base with treemanifest knowledge.

policy: relax the default for in-place build We're going to make the 'c' policy more strict, where no missing attribute will be allowed. Since we want to run 'hg bisect' without rebuilding the C extension modules, we'll need a looser policy for development environment. The default for system installation isn't changed. Note that the current 'c' policy is practically 'allow'-ish as we have lots of adhoc fallbacks to pure functions.