When getpwuid() on the system returned NULL (e.g. the user is not
in the /etc/passwd file or other uid-to-name mappings), the
codepath to find who the user is to record it in the reflog barfed
and died.  Loosen the check in this codepath, which already accepts
questionable ident string (e.g. host part of the e-mail address is
obviously bogus), and in general when we operate fmt_ident() function
in non-strict mode.

* jk/ident-loosen-getpwuid:
  ident: loosen getpwuid error in non-strict mode
  ident: keep a flag for bogus default_email
  ident: make xgetpwuid_self() a static local helper