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

- create AutoLoad env in system profile
- check for invoking .OptRequireMethods/.First/.First.sys/.Last
- remove handler-based setting of R options and align initial settings with GnuR
- create dummy .so files for utils and methods
- add -R:Rdebug option to allow debugging system profile functions