[batch] prevent ^ from counting as an escape for %

[God-damnit-all]

In batch scripts (but not on the command line itself), % is only escaped by another %

You can test this by making a bat file that reads:

@echo off
setlocal
set var=A
if ^A==A echo test1
if ^%var%==A echo test2
if "^A"==^"^^A^" echo test3
if "^%var%"==^"^^%var%^" echo test4
if "^%%var%%"==^"^^%%var%%^" echo test5
endlocal
pause

[michaelblyons]

Can you add regression tests?

[deathaxe]

Thank's for taking care and contributing. I hope it is not too aggressive to have added some arbritary syntax tests to verify the fix and help not regressing it by future changes.