Added regression tests for compound comparisons.

Added regression tests for compound comparisons.
-- Fixed several bugs associated with compound compares:
    e.g.  x = (a != b);
   (At least 4 people reported this)
-- Fixed bug associated with an empty main block (Reported by Ralf Forsberg)
-- Bank selection was handled improperly for CALL's
   (Reported by Matt W. at solid-state-logic)
-- For the PIC port, declaring variables at absolute addresses no
   longer automatically makes the variable volatile.

git-svn-id: https://sdcc.svn.sourceforge.net/svnroot/sdcc/trunk/sdcc@2052 4a8a32a2-be11-0410-ad9d-d568d2c75423