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.