merge(third_party/git): Merge squashed git subtree at v2.23.0

Merge commit '1b593e1ea4' as 'third_party/git'

third_party/git/Documentation/git-mailsplit.txt

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+git-mailsplit(1)
+================
+
+NAME
+----
+git-mailsplit - Simple UNIX mbox splitter program
+
+SYNOPSIS
+--------
+[verse]
+'git mailsplit' [-b] [-f<nn>] [-d<prec>] [--keep-cr] [--mboxrd]
+		-o<directory> [--] [(<mbox>|<Maildir>)...]
+
+DESCRIPTION
+-----------
+Splits a mbox file or a Maildir into a list of files: "0001" "0002" ..  in the
+specified directory so you can process them further from there.
+
+IMPORTANT: Maildir splitting relies upon filenames being sorted to output
+patches in the correct order.
+
+OPTIONS
+-------
+<mbox>::
+	Mbox file to split.  If not given, the mbox is read from
+	the standard input.
+
+<Maildir>::
+	Root of the Maildir to split. This directory should contain the cur, tmp
+	and new subdirectories.
+
+-o<directory>::
+	Directory in which to place the individual messages.
+
+-b::
+	If any file doesn't begin with a From line, assume it is a
+	single mail message instead of signaling error.
+
+-d<prec>::
+	Instead of the default 4 digits with leading zeros,
+	different precision can be specified for the generated
+	filenames.
+
+-f<nn>::
+	Skip the first <nn> numbers, for example if -f3 is specified,
+	start the numbering with 0004.
+
+--keep-cr::
+	Do not remove `\r` from lines ending with `\r\n`.
+
+--mboxrd::
+	Input is of the "mboxrd" format and "^>+From " line escaping is
+	reversed.
+
+GIT
+---
+Part of the linkgit:git[1] suite