Revert inadvertant changes to e2fsprogs instructions

was r11431.

chapter06/e2fsprogs.xml

@@ -50,7 +50,10 @@ cd build</userinput></screen>
 
     <para>准备安装 E2fsprogs：</para>
 
-<screen><userinput remap="configure">../configure --prefix=/usr           \
+<screen><userinput remap="configure">LIBS=-L/tools/lib                    \
+CFLAGS=-I/tools/include              \
+PKG_CONFIG_PATH=/tools/lib/pkgconfig \
+../configure --prefix=/usr           \
              --bindir=/bin           \
              --with-root-prefix=""   \
              --enable-elf-shlibs     \
@@ -61,7 +64,6 @@ cd build</userinput></screen>
 
     <variablelist>
       <title>环境变量和配置选项的含义：</title>
-<!--
       <varlistentry>
         <term><parameter>PKG_CONFIG_PATH, LIBS, CFLAGS</parameter></term>
         <listitem>
@@ -69,7 +71,7 @@ cd build</userinput></screen>
           <xref linkend="ch-tools-util-linux"/> 软件包。</para>
         </listitem>
       </varlistentry>
--->
+
       <varlistentry>
         <term><parameter>--with-root-prefix=""</parameter> 和
               <parameter>--bindir=/bin</parameter></term>