Improve regconst ispec coercion handling
Improve regconst ispec coercion handling

Allow simultaneous "allow const" and "require temporary register" meaning that
the only regconst rejected is a non-temp register (register-bound identifier).

harold-b/duktape,harold-b/duktape,svaarala/duktape,tassmjau/duktape,jmptrader/duktape,jmptrader/duktape,harold-b/duktape,markand/duktape,tassmjau/duktape,svaarala/duktape,tassmjau/duktape,harold-b/duktape,zeropool/duktape,zeropool/duktape,tassmjau/duktape,svaarala/duktape,svaarala/duktape,tassmjau/duktape,svaarala/duktape,markand/duktape,harold-b/duktape,markand/duktape,markand/duktape,markand/duktape,markand/duktape,jmptrader/duktape,harold-b/duktape,jmptrader/duktape,zeropool/duktape,zeropool/duktape,tassmjau/duktape,svaarala/duktape,tassmjau/duktape,jmptrader/duktape,zeropool/duktape,jmptrader/duktape,markand/duktape,harold-b/duktape,jmptrader/duktape,tassmjau/duktape,svaarala/duktape,markand/duktape,jmptrader/duktape,harold-b/duktape,zeropool/duktape,zeropool/duktape,markand/duktape,zeropool/duktape,harold-b/duktape,zeropool/duktape,harold-b/duktape,svaarala/duktape,markand/duktape,tassmjau/duktape,svaarala/duktape,jmptrader/duktape,jmptrader/duktape,zeropool/duktape,tassmjau/duktape