Added functions for storing/loading flagged attributes according to user-defined key.

Documentation will be updated soon (documentation of this module is out of date and
needs to be completely rewritten).
solves SER-252

db/schema/extra_attrs.xml

@@ -0,0 +1,60 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE table PUBLIC "-//iptel.org//DTD DBSchema V1.0//EN"
+  "http://iptel.org/dbschema/dtd/1.0/dbschema.dtd" [
+
+<!ENTITY % entities SYSTEM "entities.xml">
+%entities;
+
+]>
+
+<table>
+    <name>extra_attrs</name>
+    <version>1</version>
+
+    <column id="extra_attrs.id">
+	<name>id</name>
+	<type>string</type>
+	<size>256</size>
+    </column>
+
+    <column id="extra_attrs.name">
+	<name>name</name>
+	<type>string</type>
+	<size>&avp_name_len;</size>
+    </column>
+
+    <column id="extra_attrs.value">
+	<name>value</name>
+	<type>string</type>
+	<null/>
+	<size>&avp_val_len;</size>
+    </column>
+
+    <column>
+	<name>type</name>
+	<type>int</type>
+	<default>0</default>
+    </column>
+
+    <column id="extra_attrs.flags">
+	<name>flags</name>
+	<type>unsigned int</type>
+	<default>0</default>
+	<description>
+	    Various flags (SER_LOAD and such).
+	</description>
+    </column>
+
+    <index> 
+		<!-- 
+		Note: we don't need unique index, but some databases require it.
+		We need only non-unique index accordind id because of reading.
+		-->
+		<unique/>
+		<name>userattrs_idx</name>
+		<colref linkend="extra_attrs.id"/>
+		<colref linkend="extra_attrs.name"/>
+		<colref linkend="extra_attrs.value"/>
+    </index>
+
+</table>