dpkg-source(1): Document interaction of --extend-diff-ignore and -i

Document what's actually being changed, and how this interacts with
previous uses of --extend-diff-ignore, before -i w/o argument.

Closes: #729874

debian/changelog

@@ -118,6 +118,8 @@ dpkg (1.17.2) UNRELEASED; urgency=low
     Wookey <wookey@debian.org> and Johannes Schauer <j.schauer@email.de>.
     Closes: #661538
   * Bump Standards-Version to 3.9.5.
+  * Document interactions of dpkg-source --extend-diff-ignore and -i in the
+    man page. Closes: #729874
 
   [ Updated programs translations ]
   * German (Sven Joachim).

man/dpkg-source.1

@@ -20,7 +20,7 @@
 .\" You should have received a copy of the GNU General Public License
 .\" along with this program.  If not, see <http://www.gnu.org/licenses/>.
 .
-.TH dpkg\-source 1 "2013-04-02" "Debian Project" "dpkg utilities"
+.TH dpkg\-source 1 "2013-12-05" "Debian Project" "dpkg utilities"
 .SH NAME
 dpkg\-source \- Debian source package (.dsc) manipulation tool
 .
@@ -182,11 +182,13 @@ filtered out of the list of files for the diff. (This list is
 generated by a find command.) (If the source package is being built as a
 version 3 source package using a VCS, this can be used to ignore
 uncommited changes on specific files. Using \-i.* will ignore all of them.)
-\fB\-i\fP by itself enables the option, with a default regex that will
-filter out control files and directories of the most common revision
-control systems, backup and swap files and Libtool build output
-directories. There can only be one active regex, of multiple
-\fB\-i\fP options only the last one will take effect.
+
+The \fB\-i\fP option by itself enables this setting with a default regex
+(preserving any modification to the default regex done by a previous use
+of \fB\-\-extend\-diff\-ignore\fP) that will filter out control files and
+directories of the most common revision control systems, backup and swap
+files and Libtool build output directories. There can only be one active
+regex, of multiple \fB\-i\fP options only the last one will take effect.
 
 This is very helpful in cutting out extraneous files that get included
 in the diff, e.g. if you maintain your source in a revision control
@@ -200,8 +202,8 @@ the necessary anchors (e.g. '(^|/)', '($|/)') yourself.
 .TP
 .BR \-\-extend\-diff\-ignore =\fIregex\fP
 The perl regular expression specified will extend the default value
-of \fB\-\-diff\-ignore\fP and its current value (if set). It does this
-by concatenating "\fB|\fP\fIregex\fP" to the existing value.
+used by \fB\-\-diff\-ignore\fP and its current value (if set). It does
+this by concatenating "\fB|\fP\fIregex\fP" to the existing value.
 This option is convenient to use in \fBdebian/source/options\fP to exclude
 some auto-generated files from the automatic patch generation.
 .TP