…c/ is not a git checkout)
The new GC needs write barriers for certain ops
… the nom branch.
…es, for example in 'install' target
…tain git versions
(The existing C<take> function still also returns lvalues... but now we can start to correct that.)
allows us to properly future-proof code by adding "is rw" where it will ultimately be needed. Also mark many of the existing core routines that are known to be "is rw".