sed: accept s///i as a synonym for s///I ("ignore case")

Signed-off-by: David A. Wheeler <dwheeler@dwheeler.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
build system: fix make gconfig

Was getting "undefined reference to symbol 'dlsym@@GLIBC_2.2.5'".

Signed-off-by: Daniel Borca <dborca@yahoo.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>