builtin-grep: pass ignore case option to external grep
builtin-grep: pass ignore case option to external grep

Don't just read the --ignore-case/-i option, pass the flag on to the
external grep program.

Signed-off-by: Robert Fitzsimons <313a8c2711273f8eaf8175c9680d4eac1a4b53aa@273k.net>
Signed-off-by: Junio C Hamano <dc50d1021234060e53ec42a77d526afa2fe07479@cox.net>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git