documentation: Preparation for 1.7.2 release.

Updates to the following:

 * poky.ent - set the variables for a 1.7.2 release
 * <manual>.xml files - Updated the manual revision history
   tables to have a 1.7.2 release entry using March of 2015
 * mega-manual.sed - Updated the 1.7.1 string to be 1.7.2 so
   the links will be local for the mega-manual.

(From yocto-docs rev: 5f0e7ccaa736ca02c24a6a8b0a48ec5161ddfc2a)

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/kernel-dev/kernel-dev.xml

@@ -61,6 +61,11 @@
                 <date>January 2015</date>
                 <revremark>Released with the Yocto Project 1.7.1 Release.</revremark>
             </revision>
+            <revision>
+                <revnumber>1.7.2</revnumber>
+                <date>March 2015</date>
+                <revremark>Released with the Yocto Project 1.7.2 Release.</revremark>
+            </revision>
         </revhistory>
 
     <copyright>