make GnuR a dependency; download, build and copy relevant binaries; support perl (via PCRE) in grep functions

Due to changes to how vector transitions are handled, a vector cannot "leave\' the vector update method in the temporary state.

Backed out WriteVariableNode and RTruffleVisitor of 919eed72e025 because of regressions on micro.intarraywrite, pathdependentloop, loop-peel2.

Simplified handling of replacement forms - assignments to temp variables no longer eagerly trigger vector state transitions.