Fix the newly introduced method GetListOfFilesInDir to not accept every

file if no extension is enforced (= restore old behaviour). (Closes: #565213)

This commit includes also:
* apt-pkg/policy.cc:
  - accept also partfiles with "pref" file extension as valid
* apt-pkg/contrib/configuration.cc:
  - accept also partfiles with "conf" file extension as valid
* doc/apt.conf.5.xml:
  - reorder description and split out syntax
  - add partfile name convention (Closes: #558348)
* doc/apt_preferences.conf.5.xml:
  - describe partfile name convention also here

And a lovely test application of course.

2 files changed, 29 insertions, 11 deletions

diff --git a/doc/apt.conf.5.xml b/doc/apt.conf.5.xml
index e568baa35..c13ad4867 100644
--- a/doc/apt.conf.5.xml
+++ b/doc/apt.conf.5.xml
@@ -21,7 +21,7 @@
    &apt-email;
    &apt-product;
    <!-- The last update date -->
-   <date>18 September 2009</date>
+   <date>16 January 2010</date>
  </refentryinfo>
  
  <refmeta>
@@ -37,16 +37,27 @@
  </refnamediv>
  
  <refsect1><title>Description</title>
-   <para><filename>apt.conf</filename> is the main configuration file for the APT suite of
-   tools, all tools make use of the configuration file and a common command line
-   parser to provide a uniform environment. When an APT tool starts up it will
-   read the configuration specified by the <envar>APT_CONFIG</envar> environment 
-   variable (if any) and then read the files in <literal>Dir::Etc::Parts</literal> 
-   then read the main configuration file specified by 
-   <literal>Dir::Etc::main</literal> then finally apply the
-   command line options to override the configuration directives, possibly 
-   loading even more config files.</para>
-
+ <para><filename>apt.conf</filename> is the main configuration file for
+   the APT suite of tools, but by far not the only place changes to options
+   can be made. All tools therefore share the configuration files and also
+   use a common command line parser to provide a uniform environment.</para>
+   <orderedlist>
+      <para>When an APT tool starts up it will read the configuration files
+      in the following order:</para>
+      <listitem><para>the file specified by the <envar>APT_CONFIG</envar>
+	 environment variable (if any)</para></listitem>
+      <listitem><para>all files in <literal>Dir::Etc::Parts</literal> in
+	 alphanumeric ascending order which have no or "<literal>conf</literal>"
+	 as filename extension and which only contain alphanumeric,
+	 hyphen (-), underscore (_) and period (.) characters -
+	 otherwise they will be silently ignored.</para></listitem>
+      <listitem><para>the main configuration file specified by
+	 <literal>Dir::Etc::main</literal></para></listitem>
+      <listitem><para>the command line options are applied to override the
+	 configuration directives or to load even more configuration files.</para></listitem>
+   </orderedlist>
+   </refsect1>
+   <refsect1><title>Syntax</title>
    <para>The configuration file is organized in a tree with options organized into
    functional groups. Option specification is given with a double colon
    notation, for instance <literal>APT::Get::Assume-Yes</literal> is an option within 
diff --git a/doc/apt_preferences.5.xml b/doc/apt_preferences.5.xml
index 159d61f2b..9a4791c08 100644
--- a/doc/apt_preferences.5.xml
+++ b/doc/apt_preferences.5.xml
@@ -53,6 +53,13 @@ earliest in the &sources-list; file.
 The APT preferences file does not affect the choice of instance, only
 the choice of version.</para>
 
+<para>Note that the files in the <filename>/etc/apt/preferences.d</filename>
+directory are parsed in alphanumeric ascending order and need to obey the
+following naming convention: The files have no or "<literal>pref</literal>"
+as filename extension and which only contain alphanumeric,  hyphen (-),
+underscore (_) and period (.) characters - otherwise they will be silently
+ignored.</para>
+
 <refsect2><title>APT's Default Priority Assignments</title>
 
 <para>If there is no preferences file or if there is no entry in the file