mergetools: avoid losing the merged version with meld Add -o $output. When using Meld as intended (merge from left and right into the center panel), the merged version is written to the wrong file without this option ($base, a temporary file, which is ignored by Mercurial). Add meld.check=changed as a secondary safety net.

templatekw: add default styles for hybrid types (issue3887) This allows elements like file_copies to be printed as 'name (source)' when used with join.