Merge branch 'fc/fast-export-persistent-marks'

Optimization for fast-export by avoiding unnecessarily resolving
arbitrary object name and parsing object when only presence and
type information is necessary, etc.

* fc/fast-export-persistent-marks:
  fast-{import,export}: use get_sha1_hex() to read from marks file
  fast-export: don't parse commits while reading marks file
  fast-export: do not parse non-commit objects while reading marks file

diff --cc fast-import.c
Simple merge