strip: make it clear that --force discards changes (issue310)

tags: catch more corruption during cache parsing (issue2779)

localrepo: don't add deleted files to list of modified/added files (issue2761) If a file is deleted (rm, not 'hg rm') from the working dir an attempt to run 'hg diff -r X', with the file being present in X will cause an abort. We didn't check if the file has been deleted from the working dir and later on tried to open it to compare with the one from X, causing the abort. This fix adds that check. Consequently, no output will be returned.