CM11 Themes: Use 32bit hash to decide if idmap should be created

Using the last modified time of the package to determine if an idmap
should be created is not always valid for system packages.  We have
observed some packages having a time stamp of 08/01/2008 even if the
package has changed.  This causes system packages, such as
frameworks-res.apk to not be properly mapped if IDs changed in this
package.

This patch will generate a 32 bit hash code based on the file's
MD5 sum.  This hash code is then provided to idmap for writing these
values into the idmap header for future comparison.

This patch requires the following change found in frameworks/native
http://review.cyanogenmod.org/62566

Change-Id: Ie9e0273aef96217f06b08774623dd5f1b290a3da