test: adjust 'cd' regexpr to match an optional canonically pathname
    
    New regexpr now correctly deals with trailing canonical pathname.
    
    Before only the following output was matched:
    (gdb) cd
    Working directory /users/foo
    
    In addition it now matches an optional trailing canonical pathname:
    (gdb) cd
    Working directory /users/foo
     (canonically /nfs/users/foo).
    
    Triggered by `realpath .` != `pwd`
    
    2013-09-10  Sanimir Agovic  <sanimir.agovic@intel.com>
    
    testsuite/
    	* gdb.base/default.exp: Adjust regexpr for 'cd' to match optional
    	canonical pathname.