.r is the default extension used widely for both, R and REBOL. This
patch attempts to guess if .r is a REBOL file by looking for the
following very common REBOL code fragments:
- `REBOL`
- `: func [`
- `make object! [`
- `context [`
If any of those is found in a .r file, it is identified as a REBOL file.
Otherwise the language for a .r file is R.
Signed-off-by: Andreas Bolka <a@bolka.at>
