Merge branch 'pb/pretty-email-without-domain-part'

The custom format for "git log --format=<format>" learned the l/L
placeholder that is similar to e/E that fills in the e-mail
address, but only the local part on the left side of '@'.

* pb/pretty-email-without-domain-part:
  pretty: add "%aL" etc. to show local-part of email addresses
  t4203: use test-lib.sh definitions
  t6006: use test-lib.sh definitions