C 1.46_03: curINC, avoid compile-time compiler internal reloads and redefinitions.

do not really delete %INC entries, only from %curINC, and sync it at inc_cleanup.
This should fix unnecessary reloads of exp. Carp during compile-time. but breaks i24
testc.sh 124
C 1.46_04: implement lexsubs for threaded perls (#130)

need to store a empty CV in this case, with a dynamic CvNAME_HEK
t/issue130.t: untodo passing 5.18thr, speed up C tests
Changes: add line for the lexsub-thr #130 fix

also note -fwalkall to be experimental
C pod: describe -fwalkall as very experimental