merge: use collections.defaultdict() for mergeresult.commitinfo
We will be storing info from mergeresult.commitinfo to mergestate._stateextras
in upcoming patches, let's make them use same structure so that we don't have to
make much efforts in transferring info from one to other.
Differential Revision: https://phab.mercurial-scm.org/D8921
#require docutils gettext
$ $TESTDIR/check-gendoc de
checking for parse errors
Die Dateien werden dem Projektarchiv beim n\xc3\xa4chsten \xc3\x9cbernehmen (commit) hinzugef\xc3\xbcgt. Um dies vorher r\xc3\xbcckg\xc3\xa4ngig zu machen, siehe:hg:`forget`. (esc)
warning: please have a space before :hg: