Merge branch 'rs/pretty'

* rs/pretty:
Fix preprocessor logic that determines the availablity of strchrnul().
Simplify strchrnul() compat code
--format=pretty: avoid calculating expensive expansions twice
add strbuf_adddup()
--pretty=format: parse commit message only once
--pretty=format: on-demand format expansion
Add strchrnul()

diff --cc strbuf.c
Simple merge