grep: add -R

grep: add -R

This adds -R option to grep similar to GNU grep. It is the same as -r
but also dereferences symbolic links to directories.

function                                             old     new   delta
grep_main                                            834     850     +16
packed_usage                                       33362   33368      +6
grep_file                                           1440    1441      +1
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 3/0 up/down: 23/0)               Total: 23 bytes

Signed-off-by: Tomi Leppanen <tomi.leppanen@jolla.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>