Add specialisation rules to simplify the IR for 'testl .. ; js ..',

Add specialisation rules to simplify the IR for 'testl .. ; js ..',
'testw .. ; js ..' and 'testb .. ; js ..'.  This gets rid of a bunch of
false errors in Memcheck of the form

==2398== Conditional jump or move depends on uninitialised value(s)
==2398==    at 0x6C51B61: KHTMLPart::clear() (khtml_part.cpp:1370)
==2398==    by 0x6C61A72: KHTMLPart::begin(KURL const&, int, int)
                          (khtml_part.cpp:1881)

(KDE 3.5.2 compiled by gcc-4.0.2, -g -O).

git-svn-id: svn://svn.valgrind.org/vex/trunk@1616