Fix various lint warnings in manuals

Fix "new sentence, new line" warnings throughout so that formatters
can produce correct spacing between sentences.

join.1
  Remove unnecessary Ns macros. These are not necessary for delimeters,
  which get special treatment.

xinstall.1
  Fix date in manual. The contents were last modified on 2016-12-03,
  so use that instead of the invalid date.

grep.1
  Fix escape sequence for `\<` and `\>`.

ed.1
  Remove spurious `\\n` escape for the null-command.

find.1

@@ -26,9 +26,9 @@ Dereference all symbolic links encountered.
 .El
 .Sh EXTENDED DESCRIPTION
 .Ar expression
-is a combination of the following primaries and boolean operators. In
-the following descriptions the number n can be replaced by +n, n, or -n,
-to mean more than, exactly, or less than n respectively.
+is a combination of the following primaries and boolean operators.
+In the following descriptions the number n can be replaced by +n, n, or
+-n, to mean more than, exactly, or less than n respectively.
 .Ss Primaries
 .Bl -tag -width Ds
 .It Fl name Ar pattern
@@ -40,14 +40,18 @@ True if the file belongs to a user for which getpwuid() returns NULL.
 .It Fl nogroup
 True if the file belongs to a group for which getgrgid() returns NULL.
 .It Fl xdev
-True. Do not enter directory on a different device.
+True.
+Do not enter directory on a different device.
 .It Fl prune
-True. Do not enter directory.
+True.
+Do not enter directory.
 .It Fl perm Ar mode
-True if permissions on the file match mode. Mode is a symbolic mode
-as used in chmod. A leading '-' in mode checks that at least all bits
-in mode are set in permissions for file. Without the leading '-' the
-permissions for file must exactly match mode.
+True if permissions on the file match mode.
+Mode is a symbolic mode as used in chmod.
+A leading '-' in mode checks that at least all bits in mode are set in
+permissions for file.
+Without the leading '-' the permissions for file must exactly match
+mode.
 .It Fl type Ar t
 True if file is of type specified by
 .Ar t .
@@ -96,22 +100,27 @@ True if file modified time is
 days.
 .It Fl exec Ar cmd [arg ...] \&;
 Execute cmd with given arguments, replacing each {} in argument list
-with the current file. True if cmd exits with status 0.
+with the current file.
+True if cmd exits with status 0.
 .It Fl exec Ar cmd [arg ...] {} +
-True. Add as many files as possible to argument list and execute when
-the list is full or all files have been found.
+True.
+Add as many files as possible to argument list and execute when the list
+is full or all files have been found.
 .It Fl ok Ar cmd [arg ...] \&;
 Prompt the user on each file encountered whether or not to execute cmd
-as with -exec. True if the user responds yes and cmd exits with status 0,
-false otherwise.
+as with -exec.
+True if the user responds yes and cmd exits with status 0, false
+otherwise.
 .It Fl print
-True. Print the path to the current file.
+True.
+Print the path to the current file.
 .It Fl newer Ar file
 True if the modification time of the current file is newer than that of
 the provided file.
 .It Fl depth
-True. Causes find to evaluate files within in a directory before the
-directory itself.
+True.
+Causes find to evaluate files within in a directory before the directory
+itself.
 .El
 .Ss Operators
 In order of decreasing precedence
@@ -121,15 +130,15 @@ True if expression is true.
 .It Ar \&! expression
 True if expression if false.
 .It Ar expression [ Fl a ] Ar expression
-True if both expressions are true. Second expression is not evaluated
-if first expression is false.
+True if both expressions are true.
+Second expression is not evaluated if first expression is false.
 .Fl a
 is implied if there is no operator between primaries.
 .It Ar expression Fl o Ar expression
-True if either expression is true. Second expression is not evaluated
-if first expression is true.
+True if either expression is true.
+Second expression is not evaluated if first expression is true.
 .El
 .Pp
-If no expression is supplied, -print is used. If an expression is supplied
-but none of -print, -exec, or -ok is supplied, then -a -print is appended
-to the expressions.
+If no expression is supplied, -print is used.
+If an expression is supplied but none of -print, -exec, or -ok is
+supplied, then -a -print is appended to the expressions.