Added check for grep and sed to build configuration
Added check for grep and sed to build configuration

Older Autotools versions seem not to check for grep and sed
automatically. They also don't provide AC_PROG_GREP and AC_PROG_SED,
so we have to use AC_CHECK_PROGS.

oschulz/databricxx,aguetlein/databricxx,aguetlein/databricxx,databricxx/databricxx,oschulz/databricxx,databricxx/databricxx