Merge branch 'db/checkout'

* db/checkout: (21 commits) checkout: error out when index is unmerged even with -m checkout: show progress when checkout takes long time while switching branches Add merge-subtree back checkout: updates to tracking report builtin-checkout.c: Remove unused prefix arguments in switch_branches path checkout: work from a subdirectory checkout: tone down the "forked status" diagnostic messages Clean up reporting differences on branch switch builtin-checkout.c: fix possible usage segfault checkout: notice when the switched branch is behind or forked Build in checkout Move code to clean up after a branch change to branch.c Library function to check for unmerged index entries Use diff -u instead of diff in t7201 Move create_branch into a library file Build-in merge-recursive Add "skip_unmerged" option to unpack_trees. Discard "deleted" cache entries after using them to update the working tree Send unpack-trees debugging output to stderr Add flag to make unpack_trees() not print errors. ... Conflicts: Makefile