ChangeLog for smoke-me/gc-gh1136+1143 branch
gc: fix wrong inf docs
test: add big gc stress test, to catch ms2 bug
gc: fix ms2 crash with stress/gc.1

Fixes #1143
gc: fix inf Memory_Block prologs, add -D traces

inf gc did not store string/pmc Memory_Block prologs (see pobj.h),
and Parrot_str_copy changed a Buffer_flag, i.e. the str->encoding
from the prev. string.
waste now more space in inf for these prologs.

All gc's are now pretty stable.
Fixes #1136 mostly, but not 100% yet.