Make the question mark (`?') a valid punctuation character.

One can now, for example, write:

.Sh EXAMPLES
Have you read the
.Xr mdoc 7 ?
.Pp
Do you like
.Fx ?

The mdoc.samples(7) page has been automatically updated to
record this change.

contrib/groff/tmac/doc-common

@@ -130,6 +130,7 @@
 .nr z, 3
 .nr z: 3
 .nr z; 3
+.nr z? 3
 .nr z( 4
 .nr z) 3
 .nr z[ 4

contrib/groff/tmac/doc-ditroff

@@ -30,6 +30,7 @@
 .\" SUCH DAMAGE.
 .\"
 .\"     @(#)doc-ditroff	5.8 (Berkeley) 8/5/91
+.\"	$FreeBSD$
 .\"
 .\" tmac.mdoc-ditroff
 .\"     %beginstrip%
@@ -64,7 +65,7 @@
 .ds nO \fR\s10
 .ds nT \s0
 .ds pA \fC\s10
-.ds Pu \fR{\ .\ ,\ :\ ;\ (\ )\ [\ ]\ \fR}
+.ds Pu \fR{\ .\ ,\ :\ ;\ ?\ (\ )\ [\ ]\ \fR}
 .ds rA \fR\s10
 .ds rT \f(CO\s10
 .ds sH \fB\s10

contrib/groff/tmac/doc-nroff

@@ -62,7 +62,7 @@
 .ds nM \fB
 .ds nO \fR
 .ds pA \fI
-.ds Pu {\ .\ ,\ ;\ :\ (\ )\ [\ ]}
+.ds Pu {\ .\ ,\ :\ ;\ ?\ (\ )\ [\ ]}
 .ds rA \fR
 .ds rT \fI
 .ds sH \fB