[BLFS] Ticket #1730: add a .xsl for returning versions

This .xsl, applied to packages.ent, takes the package name as
a string param, then returns:
"version"<nl>"installed version" if both versions are known
"version"<nl>0 if the package is known but not installed
nothing if the package does not exist (case of the groupxx ones)

BLFS/xsl/get_version.xsl

@@ -0,0 +1,31 @@
+<?xml version="1.0"?>
+
+<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
+    version="1.0">
+
+  <xsl:output method="text"/>
+
+  <xsl:param name="package" select="'gcc'"/>
+
+  <xsl:key name="depnode"
+           match="package|module"
+           use="name"/>
+
+  <xsl:template match="/">
+    <xsl:apply-templates select="key('depnode',$package)"/>
+  </xsl:template>
+
+  <xsl:template match="package|module">
+    <xsl:value-of select="./version"/>
+    <xsl:text>&#xA;</xsl:text>
+    <xsl:choose>
+      <xsl:when test="./inst-version">
+        <xsl:value-of select="./inst-version"/>
+      </xsl:when>
+      <xsl:otherwise>
+        <xsl:text>0</xsl:text>
+      </xsl:otherwise>
+    </xsl:choose>
+  </xsl:template>
+
+</xsl:stylesheet>