Code Review 7110017: is_headless_jre should be updated to reflect the new,location of awt toolkit libraries

[Chris Hegarty]

With the changes proposed by CR 7110002: "Rename xawt/libmawt.so and
headless/libmawt.so so they can be colocated with libawt",
os::is_headless_jre() will have to be updated to look for the renamed
awt toolkit libraries. See the discussion on awt-dev for further 
information:
   http://mail.openjdk.java.net/pipermail/awt-dev/2011-November/002026.html

The check for the motif toolkit can also be removed as the motif based
toolkit has been removed in JDK7.

Since is_headless_jre is checking is for headless and short circuits
and returns false ( headed ) if it finds any headed library we can
just check for the existence of either the new or old library, without
JDK version specific code. If either exists then it is a headed
environment.

Webrev:
   http://cr.openjdk.java.net/~dholmes/7110017/webrev/

-Chris.

P.S. Thanks to David Holmes for helping drive this on the vm side.