Several trivial documentation touch ups.

  Move incorrect asciidoc level 2 titles back to level 1.

  Show output of git-name-rev in man page example.

  Reword sentences that begin with a period (.) in asciidoc
  numbered lists to work around conversion to man page bug.

  Mention that git-repack now calls git-prune-packed
  when the -d option is passed to it.

  [imap] section headers in the config file example need to be
  contained in a literal block.  imap.pass is the proper config
  file variable to use, not imap.password.

Signed-off-by: Sean Estabrooks <seanlkml@sympatico.ca>
Signed-off-by: Junio C Hamano <junkio@cox.net>