Commit Briefs
fix deletion of branches stored in packed-refs
broken since 29606af7a3a58767bf817a38035490899609d13e
revert c191ed664f6c437ebc3e0c859c53e48b445401f1
'got ref' should only work with naked ref names; implicitly putting things into 'refs/heads' is a job for something like a 'got branch' command.
got_error_from_errno -> got_error_prefix_errno
also add got_error_prefix_errno2 and got_error_prefix_errno3 which should hopefully all be merged into a single function with variadic args (but can't alloc mem)