man: Update notmuch-dump(1) and notmuch-restore(1)

Describe the new batch-tag format.  For notmuch-restore, rather than
half-heartedly duplicating the description, we now cite notmuch-dump.

man/man1/notmuch-dump.1

@@ -64,13 +64,16 @@ and tags containing whitespace or non-\fBascii\fR(7) characters.
 Each line has the form
 
 .RS 4
-.RI "+<" "encoded-tag" "> " "" "+<" "encoded-tag" "> ... -- " "" " id:<" encoded-message-id >
+.RI "+<" "encoded-tag" "> " "" "+<" "encoded-tag" "> ... -- " "" " id:<" quoted-message-id >
 
-where encoded means that every byte not matching the regex
+Tags are hex-encoded by replacing every byte not matching the regex
 .B [A-Za-z0-9@=.,_+-]
-is replace by
+with
 .B %nn
-where nn is the two digit hex encoding.
+where nn is the two digit hex encoding.  The message ID is a valid Xapian
+query, quoted using Xapian boolean term quoting rules: if the ID contains
+whitespace or a close paren or starts with a double quote, it must be
+enclosed in double quotes and double quotes inside the ID must be doubled.
 The astute reader will notice this is a special case of the batch input
 format for \fBnotmuch-tag\fR(1); note that the single message-id query is
 mandatory for \fBnotmuch-restore\fR(1).

man/man1/notmuch-restore.1

@@ -57,10 +57,8 @@ sup calls them).
 The
 .B batch-tag
 dump format is intended to more robust against malformed message-ids
-and tags containing whitespace or non-\fBascii\fR(7) characters.  This
-format hex-escapes all characters those outside of a small character
-set, intended to be suitable for e.g. pathnames in most UNIX-like
-systems.
+and tags containing whitespace or non-\fBascii\fR(7) characters.  See
+\fBnotmuch-dump\fR(1) for details on this format.
 
 .B "notmuch restore"
 updates the maildir flags according to tag changes if the