keystore: add plaintext module

Deactivated by default since secret is not encrypted.

To use it (for test purpose only):
./vlc --keystore=plaintext --keystore-plaintext-file=<my_file> <url>

modules/MODULES_LIST

@@ -201,6 +201,7 @@ $Id$
  * kai: OS/2 audio output
  * karaoke: simple karaoke audio filter
  * kate: kate text bitstream decoder
+ * keystore_plaintext: store secrets in a plaintext file (insecure)
  * kva: OS/2 video output
  * libass: Subtitle renderers using libass
  * libbluray: Library to access Blu-Ray drives

modules/Makefile.am

@@ -32,6 +32,7 @@ include control/Makefile.am
 include demux/Makefile.am
 include gui/Makefile.am
 include hw/vdpau/Makefile.am
+include keystore/Makefile.am
 include logger/Makefile.am
 include lua/Makefile.am
 include meta_engine/Makefile.am

modules/keystore/Makefile.am

+keystoredir = $(pluginsdir)/keystore
+
+libplaintext_keystore_plugin_la_SOURCES = keystore/plaintext.c
+keystore_LTLIBRARIES = libplaintext_keystore_plugin.la