Some merges can result in file being absent form working directory. This can be
one of file was kept deleted or file was removed by merge code.
User might revert the file back before committing. In such cases we will like to
have better handling and create new filenodes.
We store this info in mergestate as commitinfo so that we can use it while
committing to create new filenode if required.
This also adds some hg debugmergestate calls to show that extras are stored in